Here are the Artist Trading Cards I finished last night at the studio, they are a mixture of collage and acrylic paint and marker.
According to http://en.wikipedia.org/wiki/Artist_trading_card:
Artist Trading Cards (or ATCs) are miniature works of art about the same size as modern baseball cards, or 2 ½ X 3 ½ inches (6cm X 9cm), small enough to fit inside standard card-collector pockets, sleeves or sheets. The ATC movement developed out of the mail art movement and has its origins in Switzerland. Cards are produced in various media, including dry media (pencils, pens, markers, etc), wet media (watercolor, acrylic paints, etc), paper media (in the form of collage, papercuts, found objects, etc). The cards are usually traded or exchanged rather than sold.