Overview
JPEG-HDR was created by Greg Ward and Maryann Simmons as a way to store high dynamic range images inside a standard JPEG file. This reduces the file size required to store HDR images compared to other HDR formats such as floating point TIFF and RGBE. It does this by first converting the image into a tone mapped version and storing a reconstructive multiplier image in APP11 markers in the same JPEG file. Ordinary viewing software will ignore the multiplier image allowing anyone to see the tone mapped version of the image.
Read more about this topic: JPEG-HDR