How to make a picture comparison slider type thingy ?

[Dicehunter]

Hi peeps, Just wondering how would I make a picture comparison slider like Nvidia do with a lot of their tech showcases, Example below and any info is appreciated

Spoiler

 

[lsg1r]

You can do this if you want to do it with html/jquery

Video is obviously going to be harder and I have no idea of how off the top of my head.