Regarding 'Inaccessibility of CAPTCHA'
Matt May, whilst at the W3C, wrote an excellent paper on the inaccessibility of the most common forms of CAPTCHAs.
However, for many this type of spam-deterrent is the only effective method they can easily implement. In order for more accessible systems to become widely used, they must first be made and published. Development of hard artificial intelligence puzzles is not an easy task, less still securing, testing and supporting such programs.
I’ve recently needed to write a more accessible test for my own websites and I decided to use the concept of simple mathematics. It’s been done before, to good effect, but some of the common implementations have security issues – one script I examined stored the answer to the puzzle in plain text in a session variable, which would allow spambots to fairly easily pull this variable and use it.
It didn’t take me very long to create a system using a randomly generated mathematical puzzle, storing a salted hashed session variable for easy validation, and with protection against the most common security errors.
Some sample source code, instructions for implementation and example usage are available in the full article: Math CAPTCHA.
Back on the topic of Matt May’s paper, I don’t think that small websites, often developed on a small budget, can be reasonably expected to implement heuristic filtering of all posts. Whilst admirable efforts like Akismet have brought a sturdy, adaptive spam filter within reach of thousands of WordPress users, users of other CMS aren’t so lucky.
Arguably, they could switch to WordPress or have a plugin developed, but if there is a solid and dependable CAPTCHA which eliminates this effort, I can certainly understand their use of it.
CAPTCHA, even with it’s inaccessibility and annoyance to users, still represents the most potent form of anti-spam technology, because it stops spammers before they have a chance to do any damage, and I for one can understand although disapprove of small businesses continuing to use it.