The following information is extracted from the JPEG JFIF header. See https://www.w3.org/Graphics/JPEG/jfif3.pdf for the JFIF 1.02 specification.
Index1 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