无论如何（命令行工具）计算.NEF（也.CR2，.TIFF）的MD5哈希，无论任何元数据？

Question

Is there anyway (commandline tools) to calculate MD5 hash for .NEF (also .CR2, .TIFF) regardless any metadata, eg EXIF, IPTC, XMP and so on?

The MD5 hash should be same once we update any metadata inside the image file.

I searched for a while, the closest solution is:

exiftool test.nef -all= -o - -m | md5

but 'exiftool -all=' still keeps a set of EXIF tags in the output file. The MD5 hash can be changed if I update remaining tags.

Answer 1

ImageMagick has a method for doing exactly this. It is installed on most Linux distros and is available for OSX (ideally via homebrew ) and also Windows. There is an escape for the image signature which includes only pixel data and not metadata - you use it like this:

identify -format %# _DSC2007.NEF
feb37d5e9cd16879ee361e7987be7cf018a70dd466d938772dd29bdbb9d16610

I know it does what you want and that the calculated checksum does not change when you modify the metadata on PNG files for example, and I know it does calculate the checksum correctly for CR2 and NEF files. However, I am not in the habit of modifying RAW files such as you have and have not tested it does the right thing in that case - though I would be startled if it didn't! So please test before use.

Answer 2

The reason that there is still some Exif data left is because the image data for a NEF file (and similar TIFF based filetypes) is located within that Exif block. Remove that and you have removed the image data. See ExifTool FAQ 7 , which has an example shortcut tag that may help you out.

Answer 3

I assume your intention is to verify the actual image data has not been tampered with.
An alternate approach to stripping the meta-data can be to convert the image to a format that has no metadata.
ImageMagick is a well known open source (Apache 2 license) for image manipulation and conversion. It provides libraries with various language bindings as well as command line tools for various operating systems.

You could try:

convert test.nef bmp:- | md5

This converts test.nef to bmp on stdout and pipes it to md5.
AFAIR bmp has no support for metadata and I'm not sure if ImageMagick even preserves metadata across conversions.
This will only work with single image files (ie not multi-image tiff or gif animations). There is also the slight possibility some changes can be made to the image which result in the same conversion because of color space conversions, but these changes would not be visible.