According to the Exif 2.2 standard, the makernote is "a tag for manufacturers of Exif writers to record any desired information. The contents are up to the manufacturer, but this tag should not be used for any other than its intended purpose." Many (but not all) vendors write the makernote in IFD (Image File Directory) format, i.e., in the same format as the rest of the Exif information is encoded. Many manufacturers apparently store a lot of information in the makernote field but unfortunately, most vendors do not publish their specifications.
The following table summarizes the structures of the MakerNote field used by some vendors.
| Make | Models | Format | Specs | Remarks |
|---|---|---|---|---|
| Canon | IFD | [2] | ||
| Casio | QV-3000EX, QV-2000UX, QV-8000SX | IFD | [4] | "Early" versions of QV-2000UX and QV-8000SX only have 4 bytes in the MakerNote field. |
| Fujifilm | IFD; starts with string "FUJIFILM" and an offset to the first IFD, offsets are relative to the beginning of the MakerNote | [1] | Fujifilm's Exif data uses Motorola alignment, but the MakerNote uses Intel alignment | |
| Minolta | IFD | [5] | MakerNote numbers are always stored in Motorola/Macintosh style | |
| Nikon | E990, D1 | IFD (from offset 0x00) | [3] | |
| Nikon | E700, E800, E900, E900S, E910, E950 | IFD; starts with string "Nikon", IFD from offset 0x08 | [1] | |
| Olympus | D450Z(C-920Z) | IFD; starts with string "OLYMP", IFD from offset 0x07 | [1] | |
| Sanyo | DSC-MZ2 | IFD | [6] | Tag 0x00ff contains the offset to the start of the MakerNote(?). The semantics of the value is different in TIFF and JPEG images |
| Sigma, Foveon | IFD; Starts with an 8-byte ID string "SIGMA\0\0\0" or "FOVEON\0\0" | [7] |
Exif.org has another table with similar info and sample pictures: Digital Camera Sample Images. According to this source, (at least some) Ricoh and Kodak cameras do not write the MakerNote in IFD format.
[1] Exif
file format by TsuruZoh Tachibanaya
[2] EXIF MakerNote
of Canon by David Burren
[3] MakerNote
EXIF Tag of the Nikon 990 by Max Lyons
[4] "MakerNote"
Exif tag of Casio by Eckhard Henkel
[5] Minolta
MakerNote by Dalibor Jeline
[6] Sanyo
MakerNote by John Hawkins
[7] SIGMA and FOVEON EXIF MakerNote Documentation by Foveon