great before/after effect

[flashpipe1]

Pretty straight-forward. A few different ways to do it, but I'd create a layer with one image and a layer with the other image and put a mask over one of the layers.

Using CS3 and AS2, I'd put an onEnterFrame on the mask layer to have it slide with the mouse. And, to make it look more like the example, put a black line and have it follow it as well.

I attached a sample clip.

If it was going to be used in a larger program, I might come up with a way to avoid using the onEnterFrame, maybe a transparent layer or something. Also, looks like they're using some easing as well to give some physics to the mask.

Lots of other ways to do it as well. Would definitely do it differently in AS3, but the concept is the same.

Hope that helps!