A method for securing a printing process of a printer having a housing with a printing chamber, a printing device, a holding device for an exchangeable magazine for holding an object to be printed on, a control and evaluation unit, and a memory, the method having the following steps: inserting a magazine having the object to be printed into the holding device; moving the holding device into the printing chamber, using an optical sensor in the housing to sense a marking on the magazine; performing a comparison of the marking on the inserted magazine sensed by the sensor with a marking stored in memory in the control and evaluation unit for a magazine permissible for the print object to be printed on; outputting an error indication if the marking of the inserted magazine sensed by the sensor does not match the marking stored in the memory for a permissible magazine.