New ideas for captchas
Our forums allow anonymous posting because that lowers the barrier for users. Some time ago I modified the forum and added a simple anti-spambot protection. The protection asks the user to enter a specific string in a field, or he wouldn’t be able to post. Recently a bot (assuming it really is a bot and not “cheap paid workers from South Africa” or something, as Mike suspected 
) broke through the protection and spammed the forums. That bot has now been banned of course, and I changed the anti-bot string. I didn’t implement a “real” captcha (autogenerated string in an image, possibly with added noise to protect against OCR software) because it would take too much time.
Our forums requires visual confirmation (captcha) when registering an account. Mike suspects that there are spambots who can break through the captcha, because there are quite a few registered users who have unusual/suspicious URLs in their profile, although they don’t post anything on the forum.
Today I suddenly came up with two ideas while thinking about captchas. Has anyone ever seen ASCII art captchas on the net? I don’t! What about captchas that are made of colored HTML table cells (to simulate pixels)? Never seen them. There are probably no spambots at the moment who can read ASCII art or colored-HTML-table-cells-”images”. So why not use them as captchas?