Slideshow with morphing transition

Most of you will know this excellent online portfolio:

http://iso50.com/iso50.html

The subtle usage of Flash is superb. The square shape of each individual image of the portfolio can morph to any of the other images. Basically, when the transition takes place, the original image first gets deleted and the empty square morphs to the shape of the next image and then the new image loads in the correct shaped square. Must be an actionscript that detects the shape of the current image + the designated image (which is variable).

Now I get the basic principle of a basic slideshow, but how did this guy get the transitions done? Any info much appreciated!