[toast0]

I imagine they save the data in case there's a question about a verification. Then they can go back to the archive and say we got these images, we took steps X and Y to validate them, so we were good. If they destroy the verification images, they wouldn't be able to defend a verification claim. OTOH, they wouldn't have to worry about the security of storage for those images. (They'd still need to worry about security of the images during processing)

[neop1x]

Once verification is done, they could copy the data into an encrypted cold storage with a very limited read access. I.e. make it easy to store but difficult to read. That way they could read data if needed in specific, limitedz audited and properly authorized, cases. It's all about a proper design.