This paper addresses the problem of quality assessment dedicated to two important applications : image compression and watermarking. This topic is nowadays of a great interest because of the limitations of the mathematical criteria used formerly for quality assessment. The main aspect of this paper is the use of psychophysical experiences in order to take into account the capacities of the Human Visual System. Two campaigns have been taken for assess quality for both compression and watermarking. The main conclusion of this work is that the metrics used to assess quality such as the PSNR are very far from the human judgment and consequently from the real assessment.