How to use checksum given by Apple after I download my photos?

zzm0dgz wrote: … I know that file error during downloading is quite rare.

That's certainly not true. Errors happen all the time.

The best correction for transfer errors would be to send two copies and compare them, but that would take ages, and you wouldn't know which one was the right one! So (in a relatively mysterious way) the bytes that make up the document are combined to form a single number that is likely unique. It's called the checksum. Then the receiving software does the same, and those checksums are compared-- way faster than comparing the whole documents.

I have no idea why you are being shown the checksum.

The document isn't really sent as a whole-- it's divided up into pieces, so resends are done just with the little packet if an error is found. There are often errors in the transmissions, but with packets and checksums, the result is almost always error free.

Same problem here.

fileChecksum is not a sha*, crc32 or any usual hash. Checked against rhash tool without success.

Ideally, I would want usable hash be it for images or zip archives so it is possible to validate no transfer error.

pdf guides don't reference fileCheksum field.

Also, it seems larger zip archives (4GB+) creates warning when testing zip validity but still extracts fine

$ zip -T iCloud\ Photos\ Part\ x\ of\ y.zip 
error: invalid zip file with overlapped components (possible zip bomb)
 To unzip the file anyway, rerun the command with UNZIP_DISABLE_ZIPBOMB_DETECTION=TRUE environmnent variable
test of iCloud Photos Part x of y.zip FAILED

zip error: Zip file invalid, could not spawn unzip, or wrong unzip (original files unmodified)

$ UNZIP_DISABLE_ZIPBOMB_DETECTION=TRUE unzip iCloud\ Photos\ Part\ x\ of\ y.zip
[ok]

Neither image exif, neither csv seems to contains the title/legend/description added in icloud.

An automatable transfer way like sftp would be nice to avoid downloading manually 50+ large files.