Abstract: A method and device for monitoring the quality of distributed digital images coded by blocks of pixels in which a false contour phenomenon may be generated when the image is reproduced. An image average for pixels represented by at least one luminance respectively chrominance components is calculated and a false contour effect on the basis of a criterion for discriminating the luminance or chrominance component difference between adjacent pixels of adjacent groups of pixels is detected in at least one reference direction of each current image. A visibility coefficient of at least one current image is calculated from the value of the image average speed vector and psycho-visual criteria relating to the existence of the false contour effect in the reference direction.