Now Playing: a couple of useful websites with downloadable images
3D pictures... decoupage... paper tole... whatever you call it, done well is is a classy, elegant card form. You can print up multiples of semi-simple images and cut away smaller and smaller sections. Then they are mounted one on top of the other with some spacer like silicon glue, pop dots, or foam tape to make an image that appears three dimensional. Some artists curl the paper slightly so it lays more naturally.
If you want to get started without figuring out for yourself what parts to cut away, try these two sites which offer free printable pages. (some offer coordinated backgrounds and inserts for the cards as well.)