To accurately and rapidly detect the movement of a target observed in the field of view of an optical detector by two successive images each formed of a matrix of pixels in the field of view of the optical detector.

A device 1 detects the movement of a target C observed in the field of view of an optical detector 2. A differential image is obtained from two successive images in the field of view, a binary image is formed from the differential image and a binary conversion threshold, moving zones in the binary image are individualized, individual envelopes surrounding the zones are determined, an overall envelope surrounding the individual envelopes is determined, and it is determined whether there is movement of the target from the individual envelopes and the overall envelope.