Comment by MegaDeKay

I've found it isn't about "perfection". It is about selecting the same tiles as an "average" person would. I might stare hard at an image, think that one of the tiles contains a tiny fragment of a traffic light, and select it. That isn't what most other people have already done, so the captcha thinks I'm a bot and gives me tougher and tougher challenges. Ever since I stopped pixel-peeping and started quickly selecting the tiles that obviously had a bus in them, the percentage of time that I've gotten by first try has gone way up.