There are three major options for printing ID cards: direct-to-card printing (DTR), thermal retransfer printing (TR), and offset printing (OP).

Direct-to-Card Printing

DTC is inexpensive and is the process often used for in-house and budget operations. Despite the price, there are several disadvantages to DTC printing. When printing directly to PVC the color rendering is not very sharp. Small imperfections in the plastic prevent a complete coating of the material, and the plastic itself is resistant to the dye. Additionally, DTC does not offer true edge-to-edge printing—there is always a thin white band at the edge of the card.

Thermal Retransfer Printing

The TR process has the card image first printed to a thin film which is then fixed to the card using a heat process. This has several advantages. The color quality is based on how film takes the dye. It is more durable (dye doesn’t scratch off the film easily). TR allows printing to the edge of the card. InstantCard uses this process due to its quality and flexibility.
Read more on TR printing.

Offset Printing

OP is of slightly higher quality than TR. However, OP may only be implemented where the PVC stock is being produced. Additionally, it does not allow you to print to either prox or RFID cards (or any sort of textured cards).