DiffWidget.js
DiffWidget is a jQuery plugin for create slider/diff viewer as at jpegmini.com. Clone it and run index.html for try.
Usage
$('#ex3').diffWidget(
{
'width': '500px',
'height': '200px',
'top': 'images/forest.jpg',
'bottom': 'images/forest_invert.jpg',
'position': '75%'
})Other
Images from flickr.com