As images are clearly a part of almost any web application (user photos, avatars, etc.), analyzing them better will always be functional for users.
Face Detection is a jQuery plugin that returns the coordinates of faces in any given image.
It uses an algorithm named CCV (a JS file that needs to be included in to the documents as well) and has callbacks on every level.
The usage is straightforward, just mention the element to be analyzed and get back the results, nothing complicated.
Compatibility: All Major Browsers