Method for checking the maintenance of register of printed images to be printed on two opposite sides of a printing material

A method for checking the register accuracy of print images to be printed onto two opposite sides of a printing substrate (07), in which the first side of the printing substrate (07) is printed in a rotary printing machine by means of a first printing unit cylinder (02), and in which the second side of the printing substrate (07), opposite the first side, is printed in the printing process by means of a second printing unit cylinder (03) cooperating with the first printing unit cylinder (02), characterized in that a print image is printed by the first printing unit cylinder (02) onto the second printing unit cylinder (03), wherein the printing substrate (07) is then printed in contact with the two cooperating printing unit cylinders (02;

• 03), in that the print image printed onto the second printing unit cylinder (03) is printed, together with the same or a different print image, to be printed by the second printing unit cylinder (03) in the production printing phase of the rotary printing machine, onto the same side of the printing substrate (07), wherein these print images printed together on the same side of the printing substrate (07) are then checked with regard to their register accuracy.