Current captcha's have some problems
Current captcha's have some serious disadvantages:
* They can completely lock out disabled users
* They can be to difficult to solve for humans in some occasions
* They can be beaten by sufficiently intelligent AI
* They can be a lot of work to create (logic/puzzle-based captcha's)
* They are obtrusive
Most of these problems can be solved to some degree with traditional image, audio or logic/puzzle based captcha's. You can provide for an audio captcha as an alternative to an image-based captcha to greatly improve accessibility to the visually impaired, as proposed by Standards Schmandards (and in use on lots of sites already). You can tweak with saturation, noise and deformation of the images and audio samples used to maximize ease of use for people and minimize robots abilities to pass the test, but the last problem remains.
They are so darn obtrusive. I myself completely understand what they are for and still find them annoying! Especially the difficult to solve ones, which make me feel I have to take an IQ test before being allowed to register. So how will people feel about them that don't understand or care why it is even necessary?
I have been coming up with an alternative to captcha's that could potentially solve the last problem while retaining the advantages of Captcha's, the ability to filter out form posts done by robots instead of legitimate human users.
Here is how I think it might work in practice.
Ofcourse, this could trigger an arms race again, but this time, we don't have to force the user to jump through any hoops. Instead, we have to capture more and better metadata while the spammers have to get better and better at emulating real user's typing characteristics. .
I'm still playing with this idea in my head. The basic implementation is not that difficult to build, but the typing characteristics analysis seems difficult. Any ideas?