Less annoying than most traditional captchas, I think it may cause problems for international users. You are asking for relatively specific words (I noted penci

Less annoying than most traditional captchas, I think it may cause problems for international users. You are asking for relatively specific words (I noted pencil, saw and puzzle) that not everybody will know. Also, the pencil sharpener on one challenge is not a common type in Europe AFAIK. Idea: why aren't you using photos instead of vector graphics? They are also much easier to create (and more difficult for a machine to recognize, especially if you add some random noise).