Feature request - total file MD5

[sebutzu]

Would it be possible to have an Extra tag (computed) = MD5 of the input file.
What I am trying to achieve is to do a one pass on the files that I import in my library, and need to have ImageDataHash (to be able to detect duplicates) but also MD5 of the total file to be able to detect changes in Metadata. I assume anyhow when computing ImageDataHash exiftool probably scans the entire file, so computing also MD5 for the entire file would not make it slower.
Of course I can easily compute this outside exiftool, but that would mean I would go another time through all the content of the file using another tool.

[Phil Harvey]

Generating an md5 for the entire file would require reading the entire file again.  I don't see this as something that makes sense to add since this would be a very uncommonly used feature and there are other utilities that can easily do this.

- Phil