Photo Coasters Durable, hard and glossy surface with cork back. They come in sets of 4 (only two are shown in this photo) and measure 3.75x3.75 inches. They're slightly more than 1/8th inch thick. Coasters require that your photo have at least 768x768 pixels. Coasters have good color reproduction, but not as accurate as photographic prints. (Gorgeous photo courtesy Moon River Photography.)