Well, I know Captchas are an invention by Carnegie Mellon guy, and we all are so proud about it and all.... but hey look at these captchas... I just can not read them!
These funny things were originally designed to identify 'human' user from a script attack. Later people wrote scripts to crack these captachas. So programmers added more complexity to make them 'unreadable' to a script. Unfortunately, we have reached the stage, where even humans can no longer read the words in those capchtas!