I understand the problem of spam on blogs or robots buying from tickets sites. (Imagine the reaction of someone in 1980 if you told them, "In 2007, we will have a big problem with robots snatching up the tickets for major public events.) But this method of putting up all squiggly letters and making the purported user match them sucks. Programs can't read the letters, but you know what...I can't either! The letters are all deliberately distorted -- so how are we supposed to tell an 'l' from an 'I'? An 'S' from an 's'? A 'W' from a 'w'? I find I miss something about 1/3 the time.
Much better idea: I was at a site the other day that instructed me: "Put the answer to 3 + 4 in the box to the left." No letter guessing involved! Rotate the questions automagically, i.e., "What is the name of the animal that says 'meow'?" and you're good to go.