Lenticular images are where two images have been combined in strips so that one image is viewed from one angle and the other from another angle. This can produce a nice effect particularly if the images are related. One example of that might be a picture of someone at a young age and another picture as an adult. Years ago I wrote a simple Perl script that takes two images as inputs and creates a third image that is a lenticular combination of both.
If you would like to try my script you can find it at https://github.com/dougtoppin/lenticular. It requires a little software knowledge to run it but I am hoping that it is useful to someone.
My intent is to evolve this into a web service to make it easier to try out. More to come on that.
Wikipedia describes lenticular images at http://en.wikipedia.org/wiki/Lenticular_printing.