PC Plus HelpDesk - issue 216
|This month, Paul Grosse gives you more insight into
some of the topics dealt with in HelpDesk and HelpDesk
From the pages of HelpDesk, we look at:
- HTML 'Alt' tags (abseiling sheep);
- Spam sifting; and,
- Images - negatives and colours - and .pngs.
From HelpDesk Extra, we look at:
- Running KNOPPIX;
- USB FlashDisk or LAN;
- Pushing or pulling data on the LAN;
- smb:/ as an alternative; and,
- Just drag and drop.
HTML 'Alt' tags
Many websites do not use the html alt tag with images
and as a result, people who either cannot download images
or have no use for them are offered little useful
information when browsing the site thus making navigation
almost, if not actually, impossible.
tag has been supported since Netscape 2 and Internet
Explorer 2 and since Netscape 4 and IE 3, moving the
mouse over an image displays the alt text in the same way
that tool-tips are; for example in the screenshot snip on
the right. Alt text is now considered 'required' if your
pages are going to be useable.
The alt text is put into the html page either as alt
text in an image properties dialogue box on your WYSIWYG
html editor or in the html code itself as follows...
alt="flock of sheep" align ="right">
would present itself as the picture on the right. Just
hover the mouse over the image if your browser does this.
have your images turned off, it will look like this...
If your alt text is particularly long, Internet Explorer
will break it up for you when displaying it like a
tool-tip but you can choose where to break it yourself by
taking the final html file, loading into notepad or
kwrite and breaking the lines yourself thus...
alt="This flock of sheep is one
that we saw when we went on
a camping and walking holiday
on the Tissington Trail in
Derbyshire in August 2003"
You have to be careful with tags though because
you can put together images with descriptions that,
whilst sounding innocent in their own right, can produce
curious effects. For example...
So, if your site is intended to be a useful and
useable source of information that is easy to navigate,
as opposed to just some pointless graphics, you need to
use the alt tags and also be careful so that their
content is not ambiguous or consists entirely of
"blue bullet, red bullet, red bullet, yellow
.png images - graceful degradation
One other thing to remember about images is the format
of them. Many people have started to use Portable Network
Graphics (.png) files and like .gif s, they carry alpha
channel (transparency) information. However, where a
pixel in a gif is just on or off, in a png, it can be set
to any level therefore drop shadows or other images can
be used so that detailed backgrounds can be made use of.
One of the principles of the Internet is that the
browsing experience should be made as good as possible
and as inclusive as possible. Unfortunately, some people
make sure that their site is aimed at only IE6 or
whatever so everybody else has to put up with a degraded
experience. The same is true with png files - not all
browsers are advanced enough to support alpha channel
levels between the extremes.
The graphic below is a png file on a blue background
and makes use of a drop shadow.
|Actual png image
||IE6 on Windows
||Konqueror: Internet ready
As you can see, under GNU/Linux (Konqueror), it
is reproduced properly but under Microsoft Internet
Explorer 6 it is not - IE6 is not as advanced at this
stage so you should really use png files without
transparency if you are to make your site available for
people with Microsoft systems that do not yet understand
how to use png files properly.
If the image of the png file on the left appears
properly, your browser is ready for this new (20th
The Problem and Existing Solutions
If you need to have your email address on a website,
you have a problem with spiders crawling for mail
addresses and this then being passed on to spammers as;
"buy our list of 10 million genuine email addresses
for only $xx"
One solution to this was to put "NOSPAM"
into the address so it might read
"joeNOSPAMbloggs@foobar.com" with the intention
of the user removing it before they sent you the mail
thus leaving "email@example.com". However,
there are programs that will remove this automatically.
Other tactics include presidents names and so on but
you are assuming that the genuine sender has the
Interestingly, I receive spam email to addresses that
have never existed - they are either guesses (find a mail
domain and prefix it with "info@",
"sales@" "admin@" and so on) or
completely made-up "o8hllln@",
"f64gopp98@" and so on. Clearly, even the
people selling the millions of email addresses are
padding out the thousands they have harvested with others
that they have just made up to fill the gaps.
Spam is effectively one of a group of email activities
that you can call "unauthorised" and therefore
use an authentication system to block unauthorised email.
Instead of trying to guess if it is unauthorised, 'know'
that it is authorised.
Body Content Filtering Systems
Normal mail filtering systems rely on trying to guess
whether or not a message is spam by looking at the type
of wording of the mail and whether there are certain
clues such has heavily disguised URLs and so on - using
escape characters instead of normal typeable characters
such as http://. If you look at the source for a lot of
spams, the 'forbidden words' are divided up with html
tags that are just made up - html that is not understood
is just ignored - so when the words are displayed, they
appear as though they were meant to by the spammer so, a
text containing the 'forbidden word'; "finance"
would appear in the email source as...
...and appear on the recipient's mail program
All the anti-spam engine needs to do is strip out the
html tags to see the message. In response to this, the
spammers have started doing the following...
so that when the anti-spam engine strips out the html,
it is left with
and is passed through. However, when the end user sees
the word is corrected by their brain.
Tackling spam this way is basically just a guessing
game with the spammers hitting the email address target
every time so, why not look at it from the other side and
make it a double bullseye to hit?
Upping the Cost of Spamming
This particular solution relies on the fact that most
(if not all) spammers will have obtained your email
address by buying it off somebody else and have never
visited your website in the first place. Simply by
visiting your website, they can authenticate themselves
by reading the string but this will up the cost of
emailing 10 million people if they have to visit all of
their websites first. If they are prepared to put this
amount of effort into contacting you, you can at least
read through it (or at least the first bit of the email)
before you delete it.
Note that this will stop email from people that have
not visited your site but the scammers (Nigerian bank
scams and so on) might well visit your site first as
there is so much more for them to gain.
Subject Line Content Requirement
The solution is to have on your website a string that
must be included in the mail - the subject line being the
easiest to see - whose inclusion is the key to going
somewhere instead of straight to the deleted folder.
If, on your website, you say...
my email address is firstname.lastname@example.org and you must include
"JD3Y" in the subject line
... then any mail that does not include this can just
be deleted. If everybody did this then spammers would
have to visit all "10 million email" addresses'
sites to find the string - they would have to know where
the sites were to start with :-).
If you are going to implement this, you need to make
sure that the known genuine senders that will fall
outside the net can get their email through so one
logical filtering procedure to set up on your mail client
- Sift out the emails from granny and others who
will forget (generate rules that look at the
sender's eamil address);
- Sift out the emails from any email newsgroups
(majordomo lists and so on - generate rules
similar to 1. above);
- Sift out the emails with the string in the
subject line and put them where you want them
(generate a rule that looks for the string in the
- Delete everything else.
By doing this, you can get your machine to sort out
the half dozen or so genuine emails from the 200 spams
you get each day.
Images - negatives and colours.
is our original photograph of the Big Ben tower
It has good highlights and shadows
and poesesses red, green and blue so we can see
what is going on when we start messing around
|If we just make a
straight negative, we see that blacks have become
whites, reds have become cyans (bus) the
blue-cyan sky has become brown (our eyes are
better able to distinguish between reds, oranges,
yellows and greens than cyans and blues - this is
why there are so many words that describe them
and so many people think that cyan is blue) and
so on. To return the colours to their individual
values (ie, red back to red and so on), we have
to rotate the hues by 180 degrees.
of doing that, we could just separate the image
in to HSL channels (Hue, Saturation and
Luminosity) and then, make a negative out of the
luminosity before recombining them back into the
composite - ie turning the HSL back into an RGB
of these methods produce the image on the right
which still has a blue sky, red bus and
yellowy-green leaves on the trees but instead of
a near-white sky at the horizon, it has turned
close to black.
the Luminosity out and processing it on its own
(thus saving having to reprocess the hue later on
in order to recover the colours of the picture)
has the advantage that we can mess around with it
in any way we like. On the right, I have
solarized (or more correctly when talking about
image processing on the computer,
pseudo-solarized) it so that the highlights
become inverted and the shadows stay the same -
it is just as easy to do the opposite, either by
inverting the pseudo-solarization transformation
graph or by inverting the luminosity image after
it has been pseudo-solarized.
the right, we have the final composite image with
the highlights, mid-tones and shadows
pseudo-solarized as you would expect but the hue
information in the colours in both the normal and
inverted portions of the image has been retained.
best works where there are bright skies and
intricate structures that protrude into them.
Whilst a lamp post is not particularly intricate,
it does demonstrate that this can work even when
the intrusion is only a pixel or two across
the right is the MI6 building.
|So, we make a copy of this and then
turn that into a greyscale image so that the
luminosity information makes sense (remember that
greens are brighter than blues and so on).
|Next, use the threshold function so
that we create a black and white mask. Here, it
is done at 50 per cent but you can use other
values if you are prepared to sort them out later
on (you could adjust the luminosity mid-point of
the image to start with so that the 50 per cent
threshold separates the image the way you want it
and then change it back later).
|Next, go back to your original
colour image and select the alpha channel (this
should be all black as you haven't got anything
masked off yet). Then, paste the threshold image
you generated into the alpha channel and, if
necessary for your image processor, combine it
with the alpha base.
With the mask in place,
you can get out of the alpha channel - you will
see that the mask outline matches your threshold
image - and then invert the masked part of the
image so that the brighter part of the image is
now effectively pseudo-solarized.
|Next, and with the mask still there,
rotate the hues by 180 degrees. In the picture on
the right, the sky has become blue again.
|Next, remove the mask and then
adjust the tone balance so that it covers the
whole range, brightening up your image.
|If you wanted the sky the other way
around, either invert your threshold mask or take
the image you have just created, invert it and
rotate the hues - you get the same result.
transformations were performed using the
HSL colour model in Micrografx Picture
Publisher. However, there are many other
colour models and the one in the GIMP is
HSV (Hue, Saturation and Value). Whilst
it is possible to invert an image and
rotate its hue or even solarize by using
masks and rotate the inverted hues to get
the images above, just taking the Value
(which very tenuously replaces the
Luminosity) and inverting that in the
same way that you would with the
Luminosity in the HSL model simply does
not work. The images on the right are the
result of inverting one or some of the
HSV images and then recombining and
whilst interesting in their own right
(and not easily reproducible using HSL),
demonstrate that you need the HSL model
to do the above properly.
Based on Debian, KNOPPIX is a GNU Linux distribution
that runs entirely off a CD ROM. It only needs you to
have a computer that will boot off the CD ROM (or a
floppy disk and then the CD ROM) and have enough RAM (I
have run it on a 200MHz Pentium MMX with 96MB of RAM with
no problems). In fact, it doesn't matter whether or not
your machine has a hard drive, it will work just as well
without it as long as it has at least 82MB of RAM or, if
you want to use it in text only mode, 20MB of RAM.
Getting a copy on CDR
First of all, you need to have a copy on CD. On the
SuperDVD this month, we have the ISO image for KNOPPIX
3.3 which you should burn to a CDR. Instructions of how
to do this are elsewhere on this disc but for those who
cannot wait, you just copy the ISO file to a suitably
large and fast drive on your computer and then burn it to
a CDR. In Nero, get rid of the Wizard and click on File/
Burn Image, select the image from where you stored it,
click on 'Write' and let it get on with it.
KNOPPIX will load up
and present a desktop environment that is very similar in
many ways to Windows. On the desktop, you will see the
trash can and any disks and other media that you might
have on that machine.
You will note that there are some - or at
least one - cryptic looking labels for your hard disks.
Instead of drive C:\, D:\, E:\, F:\ and so on, where, say
C:\ and D:\ are the same physical drive with two
partitions and E:\ and F:\ are another drive with two
partitions, you will see something else. Physical drives
are given letters and the partitions are given numbers.
So, in this case, C:\ will be hda1, D:\ will be hda2, E:\
will be hdb1 and F:\ will be hdb2. If you have a usb
drive - whether it is a flash drive or a large external
drive - it should be called sda1 (and so on).
the bottom is the taskbar and if you click on the 'K' on
the far left, you get a menu like the Start menu in
USB FlashDisk or LAN
For backing up or rather, recovering data, the big
question is: "Ethernet or sneakernet?" If you
have a LAN that you can plug the computer into,
everything is a lot easier to do even if it is just one
other machine and a crossover link. If you have not, you
will have to use some other form of storage device to act
either to hold the lot or as a bucket brigade to ship the
data chunk by chunk to another machine.
A bit about the GNU/Linux file system compared to
Windows uses the drives as a root to
the directory tree and more recently, has the desktop as
the tree root with My Computer and Network Neighbourhood
running off that with the drives under My Computer and
other network shares under Network Neighbourhood. (This
is ignoring all of the other stuff in there like recycle
bins and so on). Thus...
GNU/Linux has a similar
directory structure with the root directory (not to be
confused with 'root') at the base of everything with
various directories off that. Within this semi-virtual/
semi-real file structure, various disks are 'mounted' in
various positions as are network shares. It is irrelevant
what file system each uses as they are considered
(broadly) equivalent by the file system. Extra drives
(those that are not part of the GNU/Linux system) are
usually mounted in a subdirectory called /mnt (the
leading slash meaning that the directory path is
The devices are to be found in a directory called /dev
so this is what you will find when you look at the
properties box - something like /dev/hda1 which will be
mounted at /mnt/hda1. If you were going to look at the
contents, you would look at where it was mounted because
there, it is translated into the file structure. If you
look at it in the /dev directory, you will see the raw
data on the disk.
If we created a directory called /lan and mounted the
network shares on that (remembering to create the
subdirectories first) we could end up with a structure
that is very easy to navigate. Thus...
Windows likes to inhabit the entire and only
partition on the first hard drive so if it is Windows
that will not boot up, it is likely that you will find
any data that you need on hda1 as the other drives should
be okay (unless you have Windows spread out and it is one
of these that has become corrupted).
FlashDisk or USB Drive
If you have a flaskdisk or another USB-based mass
storage device, it will probably appear on the desktop as
sda1. Before you click on it, you want to make sure that
it is mounted into the operating system as writeable
rather than read-only.
Right-click on the icon (sda1) and
then, in the Device tab, uncheck the Read Only checkbox.
Click OK and then click on the desktop icon to mount it
and display it in the file browser
Setting up the LAN
If your LAN uses DHCP (Dynamic Host
Configuration Protocol), all you have to do is click on
the KNOPPIX penguin on the taskbar - the second from the
left - and select Network/Internet | Network card
configuration and when asked if you want to use DHCP
broadcast, click 'yes' - the computer will do the rest.
If your LAN does not use DHCP or
you want to specify the settings yourself, click on the
KNOPPIX penguin on the taskbar, select Network/Internet |
Network card configuration and when asked if you want to
use DHCP broadcast, click 'no'. Next, enter the IP
address - eth0 is the ethernet card (it might be that you
are using something different or that you have two cards
(if it is the latter and you don't know which is eth0,
set up eth0 and if it does not work, you can go back to
this dialogue as many times as you like until it works
the way you want it)). Next, enter the network mask - it
will guess at this (see previous PC Plus HelpDesks for
how) - then the broadcast address, the default gateway
and the name servers and then it will set up the card for
Just to test it out, load up a copy
of Konqueror and point it at a webserver
Pushing or pulling data on the LAN
GNU/Linux was built from the bottom up with networking
and compatibility in mind therefore it has a lot of
options of how to transfer data. You can either pull it
across the network using FTP from another machine or you
can use Server Message Block (SAMBA) to push data to a
Windows machine. If you have your network neighbourhood
configured, you already have SAMBA. Otherwise you need to
set up network neighbourhood on Windows.
smb:/ as an alternative
familiar with typing http:// at the address bar of
Internet Explorer or their favourite browser but in
GNU/Linux, there are more options. In issue 214, we
mentioned KIOSlaves. Here, we are going to use one. If,
on the KNOPPIX machine, we type smb:/, we should be able
to navigate our way to the target machine by selecting
workgroup, machine, share and so on - eventually leaving
us with a window that we can see the contents of - files
If you encounter the problem of having navigated part
of the way to your destination, only to be told that you
cannot get there for some reason (not found and so on),
try deleting the workgroup name in the address thus:
if you are copying the files to a drive on the machine
you are running KNOPPIX on, do not copy to a partition
that is formatted as NTFS unless you know for sure (have
checked yourself) that the version of GNU/Linux you are
using will write safely to NTFS. As an aide-mémoire,
think of NTFS as Not That File System.
Just drag and drop
If you have two browser windows open, one at
your source directory and one at your destination
(whether it is an smb connection across your LAN or
directly onto an sda or another hda) you can now simply
highlight the files you want, drag them from one browser
window and drop them into the other.
With your files now safe, you can locate SCANDISK, if
you have not already (use the find option in KDE under
the Tools menu) and then you are ready to start
recovering your Windows functionality.
One word of warning - whilst you are in
KNOPPIX, your hard drive is protected so that you cannot
damage it (unless you have made it writeable) so you have
an unfamiliar, professional operating system that is free
to explore. In the games menu, under 'Tetris-like', you
will see a game called 'Frozen Bubble'. By all means,
have a play with it but when you realise that you can
hear the dawn chorus outside, remember that this is
highly addictive and you should limit your time spent
playing with it (strictly). For those who are
morbidly curious, the screenshot on the right is at level
You might toying with the idea that you prefer
GNU/Linux over Windows any way and decide to install it
instead - with KNOPPIX, you have an opportunity to play
around and get a feal for it without damaging your
existing installation (such that it is).
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