Technology.am (Apr.20 , 2009) — Google, which already devoted a lot of resources to block e-mail and Web spam, has tried a new test to keep the bots at bay.
Google authors have described the image-orientation technique. This task requires analysis of the often complex contents of an image, a task which humans usually perform well and machines generally do not.
A large repository of images are given from a web search result, we use suitable automated orientation detectors to prune those images that can be automatically set upright easily. We then use a social feedback mechanism to assert that the remaining images have a human-recognizable upright orientation.
The test is the latest variation on a screening technique called a Captcha (completely automated public Turing test to tell computers and humans apart). The idea is that people can often tell which way is up in a photo, but computers have a harder time.
The main advantages of the Captcha technique over the traditional text recognition techniques are that it is language-independent, does not require text-entry, and employs another domain for Captcha generation beyond character obfuscation. This Captcha lends itself to rapid implementation and has an almost limitless supply of images.