Not sure if I found this here originally but I figured I'd post it before getting it off the desktop:
http://g0tmi1k.blogspot.com/2011/04/video-playing-with-traffic-squid.html
It outlines how to set up your router to hijack web traffic to blur, flip and convert images to ASCII - among other things.
A friend and I once decided to convert an entire site of ours into ASCII art. We thought we'd do it for people on slower connections that couldn't wait for all of the pictures to load.
It looked great, but it turns out you needed a much better connection for the ASCII art than you did for the real site with photos/images etc.