A lenticular image is an image that looks different depending on how you look at it.
photojojo published a tutorial on how to make such an image.
I already did the first steps:
From those images
I created this one ;-)
I just have to print the picture, to cut it, fold it, stuff it into the frame … ;-))
By the way, I ‘cut’ the pictures in stripes with the help of Splitz, a little freeware program. That was faster ;-) (Links see below)
Links:
4 Easy Steps to Making Old-Fashioned Lenticular Images from Your Photos
Wikipedia entry: Lenticular image