wimlib

For deduplication, wimlib already has the sha-1 checksum of each file. Am I right?
So what is the --check option for? A sha-1 for the whole archive or per image?

WIM archives contain the SHA-1 message digest of each file (actually, each stream of each file; a file might contain multiple streams), and wimlib always verifies these when extracting. The metadata resource for each image is also checksummed in the same way. You can also manually verify all checksums using the 'wimverify' command.

What the --check option does is add an additional "integrity table" that contains SHA-1 message digests over the raw data of the WIM archive. In some ways this is redundant, but it's an additional option for those who want it.

It's a pleasure to test your program. Your support also really makes happy