Os saco yo rapido de dudas, el TIFF guarda siempre, el Jpeg no siempre ademas lo especifican bien claro:
formatting link
X?FF?, SOI
X?FF?, APP0, length, identifier, version, units, Xdensity, Ydensity, Xthumbnail,
Ythumbnail, (RGB)n
length (2 bytes) Total APP0 field byte count, including the byte
count value (2 bytes), but excluding the APP0
marker itself
identifier (5 bytes) = X'4A', X'46', X'49', X'46', X'00'
This zero terminated string ("JFIF") uniquely
identifies this APP0 marker. This string shall
have zero parity (bit 7=0).
version (2 bytes) = X'0102'
The most significant byte is used for major
revisions, the least significant byte for minor
revisions. Version 1.02 is the current released
revision.
units (1 byte) Units for the X and Y densities.
units = 0: no units, X and Y specify the pixel
aspect ratio
units = 1: X and Y are dots per inch
units = 2: X and Y are dots per cm
El paste me sale una chapuza, espero que cuando se postee el mensaje salga mejor, observa la cabecera de "0 no units", hay lo explica todo.