Up CAPTCHA? A CAPTCHA Based On Image Orientation
Abstract: We present a new CAPTCHA which is based on identifying an
image's upright orientation. This task requires analysis of the often complex contents
of an image, a task which humans usually perform well and machines generally do not.
Given a large repository of images, such as those from a web search result, we use a
suite of automated orientation detectors to prune those images that can be
automatically set upright easily. We then apply a social feedback mechanism to verify
that the remaining images have a human-recognizable upright orientation. The main
advantages of our CAPTCHA technique over the traditional text recognition techniques
are that it is language-independent, does not require text-entry (e.g. for a mobile
device), 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. We conducted extensive experiments to measure the viability
of this technique.