"Seam Carving" is a technique for resizing images based on "seams". Seams are runs of similar pixels, and are identified by using gradient magnitude. When you cut out less significant pixels in a seam, you end up being able to resize an image in a non-uniform manner, but retain important features. You can even use it to remove items, like say an ex from that last vacation...
It is a lot easier to see it in action. Take a look:
Larry O'Brien talks about the algorithms behind this here. I had never heard of A* before this. Interesting stuff.