It should work reliably but only with "modern" jpeg files. Older files have a slightly different (shorter; no exif stuff) header that makes them more ambiguous.

It should work reliably but only with "modern" jpeg files. Older files have a slightly different (shorter; no exif stuff) header that makes them more ambiguous. So some of those might not get detected properly but it should work for anything taken by a modern camera/phone. PNGs should always work as that format is very easy to detect.