I dislike like long, nonsensical captchas that confuse people, it's totally annoying. A few years ago i used a 5 digit captcha, but in the background i added faded small letters in various angles.
Unfortunately the faded small letters probably did not make your captcha more difficult to crack. It's relatively simple to remove all grey pixels from the image before OCRing it.
However having your own custom captcha probably helped quite a bit. I'm guessing spammers aren't going to bother writing custom software to decode your captcha unless you have a major site.
Yes of course. But you can choose certain colors, not gray that look faded to the eye but are not in rgb values. In any case, captchas are always mediocre solutions.
