These home-made small cards have a special size which is always the same : 64 mm x 89 mm.
They can be made using different techniques (painting, inking, embossing, crayoning, printing, stamping, collage, transfer, digital picture…) and materials (paper, cardboard, shaped hot glue, leaves, buttons, iron wire, string, tissu…).
Usually they are not for sale. ATC lovers exchange them and collect them.