SPIF

SPIF (Streaming Progressive Image Format; not to be confused with SPIFF) is an experimental multi-resolution image file format, along with a JavaScript library that helps to make efficient use of it on the web.

A SPIF file appears to be essentially a "container" or "archive" file, containing multiple independent JPEG files.

Sample files

 * https://github.com/kig/multires/blob/master/spif/test.spif

Links

 * SPIF website
 * Source code at GitHub