Another technique to combat comment spam in your blog is to add some fields to your blog's comment form that cannot be seen. I am not talking about HIDDEN fields, although those might work in some cases (I have no idea how smart spambots are). A clever technique that I had not seen before in the above blog post sets the CSS style for these extra fields to invisibility. With a separate stylesheet,the common spambot might not ever realize that it is filling in a field that a human or other sentient would never see. You can just accumulate the comment spam in your database while hiding it from view (the approach taken above), but if you can modify your blog software, then comment spam can just be ignored before it makes it out to the database – that is what I would do. In any case, another tactic to combat comment spam (and less annoying than some CAPCHTAs).
Anyway, that's not what I wanted to comment on. What I did want to say, is that another link found on Reddit, a "movie", clearly showed that with tools currently in use by comment spammers, captchas are easily bypassed, completely automatically. A test shows a submit of the same post on 400 different forums in about 10 minutes time.
Re:What about those with Visual Disabilities?
barbie on 2007-02-04T11:06:33
Instead of making the form field invisible, create a div that's invisible via CSS, with text and the form field. The text then noting that the field is for spam prevention and is not to be filled in. That way anyone using a screen reader or not CSS enabled, can understand why the field is there.
DVD John's blog uses WP-Hashcash which is another interesting idea adapted from email spam ideas. I don't know how it degrades for those who don't have Javascript, though.
Basically, submitting a comment requires your browser to devote a certain number of processor cycles to calculating something that is quickly verifiable by the server.
