ExifTool Forum

I looked and couldn't find a tag that includes the byte count offset and length of bytestream of the primary image.

I'd like to be able to take a SHA256 of the image, after omitting all metadata. Is there an efficient way to do this?

Thanks for your time and efforts!

You can get an MD5 like this:

exiftool -imagedatamd5 FILE

- Phil

Quote from: mceachen on April 12, 2023, 01:41:39 AMI looked and couldn't find a tag that includes the byte count offset and length of bytestream of the primary image.

There isn't one that I recall and if there was, then Phil would have mentioned it.

QuoteI'd like to be able to take a SHA256 of the image, after omitting all metadata. Is there an efficient way to do this?

If you need SHA256 instead of MD5, take a look at this post (https://exiftool.org/forum/index.php?topic=9722.0), which was the old way of doing a MD5 hash.

Alternatively, you could parse the output of the -v3 (-verbose3) option (https://exiftool.org/exiftool_pod.html#v-NUM--verbose).  It won't give exact image starting point, but that could be computed.  JPEG SOS is Start of Scan (I think) and JPEG EOI is End of Image

Example:
C:\Programs\My_Stuff>exiftool -G1 -a -s -e -v3 y:\!temp\Test4.jpg
  ExifToolVersion = 12.60
  FileName = Test4.jpg
  Directory = y:/!temp
  FileSize = 445460
  FileModifyDate = 1680707743.45783
  FileAccessDate = 1681311542.93255
  FileCreateDate = 1680222709
  FilePermissions = 33206
  FileType = JPEG
  FileTypeExtension = JPG
  MIMEType = image/jpeg
JPEG DQT (65 bytes):
    0006: 00 02 01 01 01 01 01 01 01 01 02 02 02 02 02 02 [................]
    0016: 02 02 02 02 03 04 05 06 04 03 04 04 05 07 06 06 [................]
    0026: 06 05 06 06 06 06 07 09 07 06 08 09 0a 09 08 0b [................]
    0036: 08 06 06 0a 0a 0a 0a 0b 0c 0b 08 09 0c 0a 0a 0a [................]
    0046: 0a                                              [.]
JPEG DQT (65 bytes):
    004b: 01 02 02 02 02 02 02 05 03 03 05 0a 07 06 07 0a [................]
    005b: 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a [................]
    006b: 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a [................]
    007b: 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a 0a [................]
    008b: 0a                                              [.]
JPEG SOF0 (15 bytes):
    0090: 08 04 b5 06 d5 03 01 22 00 02 11 01 03 11 01    [.......".......]
  ImageWidth = 1749
  ImageHeight = 1205
  EncodingProcess = 0
  BitsPerSample = 8
  ColorComponents = 3
  YCbCrSubSampling = 2 2
JPEG DHT (28 bytes):
    00a3: 00 00 02 02 02 03 01 01 00 00 00 00 00 00 00 00 [................]
    00b3: 00 02 03 01 04 00 05 06 07 08 09 0a            [............]
JPEG DHT (90 bytes):
    00c3: 10 00 02 02 01 03 02 04 04 03 06 05 03 01 00 02 [................]
    00d3: 23 01 02 03 11 00 04 12 21 31 41 05 06 13 51 07 [#.......!1A...Q.]
    00e3: 22 61 71 08 32 81 09 14 91 a1 c1 f0 23 42 b1 d1 ["aq.2.......#B..]
    00f3: e1 15 52 f1 33 62 16 17 18 24 72 0a 82 25 43 92 [..R.3b...$r..%C.]
    0103: 19 34 a2 e2 26 53 a3 b2 c2 d2 1a 27 28 54 b3 c3 [.4..&S.....'(T..]
    0113: d3 35 36 44 45 63 73 74 83 93                  [.56DEcst..]
JPEG DHT (26 bytes):
    0121: 01 00 02 03 01 01 01 01 00 00 00 00 00 00 00 00 [................]
    0131: 00 01 02 00 03 04 05 06 07 08                  [..........]
JPEG DHT (65 bytes):
    013f: 11 00 02 02 01 03 02 04 02 09 02 05 03 04 02 00 [................]
    014f: 07 00 01 02 11 21 03 12 31 04 41 05 22 51 61 13 [.....!..1.A."Qa.]
    015f: 71 06 14 32 81 91 a1 b1 c1 f0 15 d1 07 23 42 52 [q..2.........#BR]
    016f: e1 24 33 f1 34 62 72 b2 25 92 16 53 43 d2 17 35 [.$3.4br.%..SC..5]
    017f: a2                                              [.]
JPEG SOS
JPEG EOI
Of course, this assumes a jpeg.

Thanks you two!

If I want to append ImageDataMD5 to the standard tags, is there a better way than using
-imagedatamd5 -all?

(Is "-all" equivalent to "-*"?)

With both -imagedatamd5 and -all on the command line you will get two copies of ImageDataMD5.  Instead, do this:

exiftool -api requesttags=imagedatamd5 FILE

- Phil

Now that ExifTool uses

-ImageHashType
instead of -ImageDataMD5, is this the proper way to do it?

exiftool -api requesttags=imagedatahash -api imagehashtype=SHA256 FILE
This seems to work, but if there's a more correct way to do this (I'm using "-stay_open True" mode, fwiw), I'm all ears.

Thanks again for the assist!

Yes, that would be the correct way to include the imagedatahash in the output without calling it specifically.

Thanks again!