Tracepaper
This is a simple application I wrote in Ruby to allow you to overlay images from two directories on top of each other as if they were on tracing paper. The top image is 50% transparent, allowing you to compare it with the other. I wrote this application to allow me to quickly sift through time-lapse phtographs to remove and replace frames that “jump.” Development has since stopped due to a significant memory leak in libgtk-ruby.
TracePaper screenshot
Source code is waiting for you here: http://github.com/mattjackets/tracepaper