A CDV is a image that was developed on a very thin sheet of paper, and then was glued to stiff card stock. Carte de visite, or CDV, actually denotes a size or format. A CDV is a specific size: 2 3/8" x 4 1/4". Note the size may vary up to 1/4", especially with early samples as the photographer may have cut his own card stock. But generally they were close in size, partly due to the standard size of album slots.