As far as I know bots, even advanced ones, have an extremely hard time with dotted fonts. Just change the Captchas to use some really dotted or unique fonts where the letters are made up of smaller elements that don't connect. You can extend the life of Captchas for a few more years.
Eventually, the spammers will make a bot to analyze the distance between dots, group them into letters, and the race will be on to use other methods. I see this as a never ending virus/immunity battle. We're pretty much at the end of Captchas. Other methods like mouse movement, surfing time, scrolling, etc... can all be mimiced as well. Computers can or will be able to simulate humans very well, even our imperfections.
You might find these examples from LeNet interesting. They are examples of unusual styles of digits that the system correctly recognized, made of dashed lines, bubbles, and dots. Granted this system only recognized digits, but it's not exactly a stretch to jump to the character set typical of Captchas.
> Eventually, the spammers will make a bot to analyze the distance between dots, group them into letters, and the race will be on to use other methods. I see this as a never ending virus/immunity battle. We're pretty much at the end of Captchas. Other methods like mouse movement, surfing time, scrolling, etc... can all be mimiced as well. Computers can or will be able to simulate humans very well, even our imperfections.
Love your optimism. I'd like to say that captchas are very limited : they have to be solvable by idiot humans. Captcha algorithms have no such limits they have to abide by. Since the anti-spam side of things is blocked at a certain point in the arms race, the other side is bound to win.
Why not just require, say, a google or facebook login and transfer the "eliminate spammers" problem onto them ?
http://yann.lecun.com/exdb/lenet/weirdos.html