How to determine what tag is the difference between these two photos?

[handvprice]

These two copies of a photo have exactly the same image, but their files differ in two bytes (at hex 0000098c and d I think). I haven't yet found what tag this represents using exiftool -a -U, or is there some other un-accounted-for info in the metadata?

(They are jpg's created by downloading a .heic from an iphone on two separate occasions, with "Transfer to Mac or PC" setting of "Automatic", which converts the .heic to a .jpg plus a .mov.)

TY. (I hope the uploaded photos maintain their metadata so you can see the difference).

[StarGeek]

The sections in question

Code Select Expand

IMG_9951 r iphone se2.JPG
0986: 00 00 00 01 00 06 76 14 02 01 00 04 00 00 00 01 [......v.........]



IMG_9951 r iphone se2 other.JPG
0986: 00 00 00 01 00 06 93 07 02 01 00 04 00 00 00 01 [................]
Using exiftool's -v (-verbose) option, the listing for that section is the same

Code Select Expand

  + [IFD1 directory with 3 entries]
  | 0)  Compression = 6
  |     - Tag 0x0103 (2 bytes, int16u[1]):
  |         098a: 00 06                                           [..]
  | 1)  ThumbnailOffset = 2462
  |     - Tag 0x0201 (4 bytes, int32u[1]):
  |         0996: 00 00 09 9e                                     [....]
  | 2)  ThumbnailLength = 25595
  |     - Tag 0x0202 (4 bytes, int32u[1]):
  |         09a2: 00 00 63 fb                                     [..c.]
Looking at the same section in a completely different images gives similar results, the two bytes after Compression are skipped.

Code Select Expand

  + [IFD1 directory with 3 entries]
  | 0)  Compression = 6
  |     - Tag 0x0103 (2 bytes, int16u[1]):
  |         098a: 00 06                                           [..]
  | 1)  ThumbnailOffset = 2462
  |     - Tag 0x0201 (4 bytes, int32u[1]):
  |         0996: 00 00 09 9e                                     [....]
  | 2)  ThumbnailLength = 25595
  |     - Tag 0x0202 (4 bytes, int32u[1]):
  |         09a2: 00 00 63 fb                                     [..c.]
In both cases, the other two tags in that section are 4 bytes.  My guess is that those two bytes are simply padding and otherwise are junk.

Phil will have to weigh in on the actual reason.

[StarGeek]

From page 38 of the EXIF 2023 standard

Value Offset
This tag records the offset from the start of the TIFF header to the position where the value itself is
recorded. In cases where the value fits in 4 Bytes, the value itself is recorded. If the value is smaller
than 4 Bytes, the value is stored in the 4-byte area starting from the left, i.e., from the lower end of the
byte offset area. For example, in big endian format, if the type is SHORT and the value is 1, it is
recorded as 00010000.H.

The Compression tag is a SHORT, only two bytes.  This pretty much fits the example here, except that instead of nulls, it appears to be random values.

As to why the two bytes are different, no idea.  Have the images been processed in anyway?

[Phil Harvey]

Phil will have to weigh in on the actual reason.

Yup.  Unused bytes are normally filled with zeros, but they don't have to be.

- Phil