As the system is driven by masks, several have been provided in the download file. These masks form the different elements that combine to form the front and back of the card. These can be completely custom of course, and you are able to replace them with any you see fit. To use these, just drag and drop the image you would like onto the shader editor while the card is selected, and plug it into the appropriate mask slot. All masks have been linked to the shader output so further shader development is possible and easy.

Note: Make sure that just before the material output, a transparency shader is mixed with the main shader using the border mask as the factor to keep the round borders of the card.