Detection of unstructured moving objects with the aid of difference images

Sensor arrangement 2 for detecting unstructured moving objects 6 in a monitoring area 4, comprising: at least one camera 8, that records images 10a-d at different times ta-d; a difference module 14 that creates difference images 16a-c from two images of different times; and a neural network 18 trained to classify 20a-c objects in the difference image. The object may be a fire feature, smoke or other damage feature such as moving water. The difference images are formed from images with a constant time difference (D) of their acquisition times (ta-d). The neural network may be a CNN trained with difference images. The classifier may contain object location data (O). A hypothesis module 22 may generate a hypothesis 26 about objects in difference images in a time window (T) using at least one classification result (20a-c). A verification module 28 may test the hypothesis using all classification results and the time points (ta-c) in the time window (T) and provides an output indicating if the hypothesis is correct. A training environment 32 may be provided to the neural network.