1. An apparatus for correlating at least two images of a photolithographic mask that at least partially overlap, the apparatus comprising: a correlation unit that is provided to use at least one random variation, which is present in the at least two images, of at least one structural element of the photolithographic mask for the correlation of the at least two images, in which the correlation unit is configured to use information about the at least one random variation of the at least one structural element in a first of the at least two images and information about the at least one random variation of the at least one structural element in a second of the at least two images to correlate the at least two images, wherein the at least one random variation of the at least one structural element forms a marker that is always present on the photolithographic mask, and thus avoiding applying a marker being visible in the at least two images for correlating the at least two images, wherein the correlation unit is provided to generate from at least a first of the at least two images a simulation of a second of the at least two images, and wherein the simulated image is used for the correlation of the first and the second image.