So what are the rules? There's only one rule:
Cards must be 2 ½ X 3 ½ inches.
That's it.
What do they look like? They are as individual as the artists who create them. They can be originals or prints. B&W or color. Paint? yes. Pencil? yes. Watercolor? yes. Collage? yes. Pen? Ink? Rubber stamps? Fabric? Metal? Digital? Yes, yes, yes...
Personally, I find they're a great way to get the creative juices flowing. I can test out ideas on something small first and play with new ideas. Sometimes, an ATC will turn out great and become the inspiration for something larger. Plus, they're deceptive. Something so small can sometimes take so much time.
They're a great way to get people thinking about art, talking about art, and even living with art. Try making a few of your own. Now what was that rule...
Art you can carry in your pocket.
What could be better?
What could be better?