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Web Bugs (also known as Web Beacons, tracking bugs, and 
pixel tags) have bothered me for years. They’re in the same category as tracking cookies, and provide similar functionality for those who use them.
What are web bugs?
Web bugs are tiny 1×1 pixel transparent images placed on web pages in order to track web page usage. They can also be placed into html-based e-mail messages in order to track 
when and where such messages are read.
To my knowledge, there aren’t any plug-ins for Firefox for detecting and/or blocking web bugs. But doing so can be somewhat problematic since tiny transparent images are sometimes used for aligning html content (although, usually, you’d find an image that was one pixel wide but many pixels long; using 1×1’s for alignment is a bit of a stretch).
Here is an example of a web bug 
found on Quicken’s website:
<img src=”http://ad.doubleclick.net/ad/pixel.quicken/NEW” width=1 height=1 border=0>
Many years ago, there was a nifty add-on for Internet Explorer called Bugnosis that worked pretty well. I don’t know whether Bugnosis is still in active development. A look at their site shows that it supports IE 5.01. Hmmm, I 
wonder if it will work on 6 or7? And I wonder if there is something like it for Firefox?
For more information…
Electronic Frontier Foundation Web Bug FAQ:
http://www.eff.org/Privacy/Marketing/web_bug.html
Web Bug Traffic Report:
http://www.securityspace.com/s_survey/data/man.200703/webbug_traffic.html
C|Net News article on web bugs:
http://news.com.com/2100-1017-243077.html
(the images in this blog entry are not web bugs, but images from the original Bugnosis website. I couldn’t do web bugs if I wanted to; WordPress forbids that and other nasty things as well)
Peter H. Gregory 