A funny technology where the cat and mouse game is extremely active is the field of Captcha. Captcha stands for Completely Automated Public Turing test to tell Computers and Humans Apart. In other words, the objective is to make a test that should differentiate a human operator from a computer. It is the test of scrambled letters that you have to type to proof that you’re not a robot. For instance, if you want to add a comment on my blog, you’ll have to answer a captcha.
Captcha initially started with a few letters. OCR solved too easily the problem. Then, the fonts were distorted, twisted, scratched… And the attackers refine their detection algorithms.
This summer, NuCaptcha, proposed a new challenge: you had to identify letters of a given color within a moving text on top of a background. It combined three challenges: identify the color (which may change for each challenge. Thus, you have to identify where the color to detect is defined), extract the text from the background, and then extract the proper letters. In some case, the background may be animated like a clip. Thus, it seems an interesting challenge.
Interestingly, since August, they added a few new solutions which were branded, or advertisement driven. Unfortunately, although they may bring some revenues, these versions have seriously impaired the difficulty of the challenges (have a look at the demo page, and make your own opinion). Would you like to use NuCaptcha, I would recommend avoiding the branded or ads versions. Most of the benefits have vanished (at least as they are presented in the demo)
Nevertheless, Captcha is an interesting tradeoff between security and usability.