The answer for JPEG XT is in Wikipedia: https://en.wikipedia.org/wiki/JPEG_XT https://en.wikipedia.org/wiki/JPEG_XT "JPEG XT extensions are backward compatibl

The answer for JPEG XT is in Wikipedia: https://en.wikipedia.org/wiki/JPEG_XT https://en.wikipedia.org/wiki/JPEG_XT "JPEG XT extensions are backward compatible with base JPEG/JFIF file format - existing software is forward compatible and can read the JPEG XT binary stream, though it would only decode the base 8-bit lossy image." It is a standardization of how to put additional data in the already existing JPEG file format, the one that we already have supported everywhere. Then, if some software "understands" what the XT parts of these JPEG files mean, it can use these new parts, still, the files are usable on every device, just these XT parts don't mean anything to the devices that don't understand XT.