I once absent-mindedly ordered Three Mile Island dressing in a restaurant and, with great presence of mind, they brought Thousand Island Dressing and a bottle of chilli sauce. Terry Pratchett on alt.fan.pratchett
CAPTCHAs Shut Out Blind Users
If anyone still has doubts about the problems that visual CAPTCHAs can create, I suggest that they check out a video produced by the American Federation for the Blind (AFB).
Entitled “CAPTCHAs on Social Networking Sites Shut Out Blind Users“, the video presents a very compelling case against purely visual challenges. However, as the video has been published via YouTube, you will need access to the Flash Player plugin in order to watch it.