Google is building what it hopes is a much less annoying replacement for CAPCHA, the mechanism that tests to see whether you are a bot or a human.

This latest version uses a much more mobile and human friendly series of puzzles. As an example, the CAPCHA might present an image of a cat along with a series of nine additional images, asking you to tap all the images that also contain cats. This turns out to be simple for a human to solve and much harder for a bot to solve than the mathematically misshapen text in a traditional CAPCHA puzzle.

Interesting article.