C'est inutile donc c'est brillant : ce site vous montre ce la dégradation subie par une image enregistrée, puis re-enregistrée, puis re-re-enregistrée... trop souvent en .jpeg :
Question: What does "needs more JPEG" mean?
A:The briliant website Knowyourmeme has a great article on the phrase "needs more JPEG". But in summary: "needs more JPEG" is an ironic phrase used after one encounters an image which has been opened and saved so many times that the image quality has been greatly reduced which is often expressed in the form of blurry artifacts and blocky images.
Question: Why do JPEG's get increasingly more artifacts after each save?
A:This is due to the fact that JPEG is a "lossy compression algorithm", meaning that not all of the original image information is kept after a save, in exchange for this you get a significant smaller file size. Every time you save a JPEG this process is repeated thus losing some more image information. Not all image formats have this problem non-lossy fileformats(also called: lossless) don't have this problem, frequently used lossless fileformats are: PNG, GIF and RAW.