Defeating 'using one server for all images' by using Junkbuster
Junkbuster's blocklist is created and editable by the user, not by, for instance, cyberpatrol. The list also has 'allow' entries. Entries are processed in order, and the last entry to match sticks. This allows the user to construct much more powerful rulesets than cyberpatrol.
Junkbuster, being an open source project, has been improved significantly since this writeup was written, and has been renamed 'Privoxy'. Text in itallics reffers to this new version, while normal text reffers to the older junkbuster, as was available at the time this writeup was initially written.
- The user can use a ruleset that blocks the entire images server, and then allows only the images that are used for navigation:
Though the user would have to discover the obfuscated names of the navigation images, it wouldn't take that much effort. This technique could be thwarted by changing the URLs used for navigation images every so often, but this would have the side effect of reducing the effectiveness of caching of your site, thereby increasing your bandwidth bill.
- Old versions of Junkbuster on their own are indeed defeated by this technique, though if Mozilla is used as a browser it can be set to prevent animated GIFs from looping, lessening the impact of the banners while leaving the navigation images unaffected. Newer versions of Junkbuster (now called Privoxy) can modify animated gifs sent to the browser, allowing this technique to be used with any web browser.
- On the one hand, there is something clever about displaying adverts in a text-based browser, but on the other hand, this is exactly what you're supposed to be doing - <ALT> tags are supposed to provide a textual description of any image that is important to the page. Arguably, the user of a text-based browser may be interested in your advert and want to view it.
If (instead of switching images off) the user of a graphical browser sets junkbuster to block the images, then they display as transparent webbugs and don't get an alt-text. Newer versions of junkbuster can edit the web page before it is passed to the browser, and so could remove your alt-text adverts from the HTML, preventing them from being displayed even on a text-based browser