The following information is extracted from the JPEG JFIF header. See http://www.jpeg.org/public/jfif.pdf for the JFIF 1.02 specification.
Index Tag Name Writable Values / Notes 0 JFIFVersion N 2 ResolutionUnit int8u 0 = None
1 = inches
2 = cm3 XResolution int16u 5 YResolution int16u
Tag ID Tag Name Writable Values / Notes 0x0010 ThumbnailImage N