Photojojo details an easy set of instructions that will let you create eye-catching photo-in-photo transparent images like the one shown above. You don't need a fancy camera or expensive software. All you need is a few extra gadgets, some creativity and a helper to snap the photos.
The process to create a transparent photo like the one above is quite easy: your helpful assistant takes a succession of photos, starting with the closeup of your eyes, and then you display the photo in position on the iPhone when you take the next shot, which gets displayed on the iPad... you get the idea. Check out Photojojo for the detailed rundown.
This is just one example. You can use this technique with different gadgets and additional layers to create captivating images. Experiment and enjoy!