Joint Photographic Experts Group (JPEG) - JPEG File Interchange Format (JFIF)
JPEG/JFIF is not a protocol, but:
- JPEG is a compression algorithm for photos.
- JFIF is a file format used to contain a JPEG photo.
JPEG / JFIF is good to use for photos, but should be avoided for diagrams, icons and alike (with hard edges and only a few colors).
Obsoleted by the ["PNG"] graphics file format, but still widely used.
JPEG isn't obsoleted by PNG. They serve different purposes and PNG doesn't come near the compression that JPEG is capable of with a small loss in image quality.
Before PNG, GIF was the recommendation for diagrams, icons and such. GIF has been obsoleted by PNG for everything, except animations, which PNG doesn't support.