1. Apparatus for detecting a change between images or in a sequence of images, each individually entropy-encoded to code blocks of variable lengths, which are allocated to different sections of the respective images, wherein the apparatus is implemented to use, for detecting the change, a measure for the change that depends on a length of the code blocks of the images, wherein the images are encoded in a manner divided into sub bands of different transformation stages by means of a wavelet transformation, and the code blocks represent entropy-encoded versions of transformation coefficient blocks of the sub bands, the apparatus comprising: an adder configured to—at least for a first and second one of the images, —for image unit regions into which the respective image is divided according to a respective spatial resolution—add the lengths of those code blocks relating to an image section according to the wavelet transformation that overlaps with the respective image unit region, in a manner weighted in dependence on a ratio of the respective image unit region to the respective image section, to acquire, for the image unit regions of the respective image, one added value each as a measure for a local entropy; and a calculator configured to calculate the measure for the change in dependence on the added values; wherein at least one of the adder and the calculator is implemented using hardware.