Taking the fear out of web application snapshot testing
Testophobia runs your web site/application in a headless web browser* and performs the UI actions that you specify, taking screenshots of the page along the way. It will compare these snapshots to previously taken versions (that are known to be correct), and validate that the page still looks and behaves as it should.
* Supports Google Chromium, Firefox, and Webkit (Safari)
Take a look at the Wiki for documentation and tutorials.
MIT