Lossy Compression
Compression that permanently discards image information judged least perceptible, in exchange for much smaller files.
Measured in
ratio
In depth
The discarded data cannot be recovered, and each successive save discards more — which is why editing a JPEG repeatedly degrades it in a way that editing a TIFF does not. Used once at a high quality setting on a finished image, the loss is genuinely invisible; used as a working format it accumulates.
Examples in practice
Opening, editing and re-saving the same JPEG ten times leaves visible blocking around high-contrast edges.