I’ve recently completed a small project for Uni; an image based CAPTCHA mechasisim I have called Jaci (Just Another Captcha Implementation). It requires you to drag and drop relevent images onto eachother in order to pass the test. The images are not static and uses Google Image Search for the source of the images.
The main motivation behind the work is a dislike for current CAPTCHA mechasisims. I have good vision and still find the common distorted word captcha frustrating at times. This test is useless for the dislexic and vision impared and creates some accessability problems that will be more and more prevailant as CAPTCHA type mechanisims are intergrated into everyday life. To read more about it, check it out here http://ryandoyle.net/devel/jaci