From Wikipedia: Artist Trading Cards (or ATCs) are miniature works of art about the same size as baseball cards (2.5 by 3.5 inches) and thin enough to fit inside standard card-collector pockets, sleeves or sheets. The ATC movement developed out of the mail art movement and has its origin in Switzerland. The cards are usually traded or exchanged rather than sold.
Here are some of my latest ones. They're not the best photos but if you click on each photo, you should be able to see the ATCs more clearly.
If you would like one, let me know. But you have to trade for them. That means you have to make one for me! Try it. It's fun..... and addicting. Some work out and some, .......... well ............ I don't throw any away because I always learn something from them, even if it's to NOT do it that way again.