I think that creating a PAR archive is probably what you're looking for.
PAR files are basically checksummed data generated from the original files. They can be used to check over a file (whether original or copy) and if any corruption is detected, the PAR file can then be utilized to correct or patch the corruption. I first came across them with files on Usenet; perhaps internet connections were flakey enough back then that you had to worry about file corruption in the upload and download process, but the PAR files worked really nicely to restore corrupted files, or regenerate files that were missing.
The Wikipedia article
mentions that they were originally used with Usenet, but are now used for things such as guarding against bit rot. So it sounds like this is exactly what you're looking for!
The program I use is MacPAR Deluxe
, which is donationware (free, no features are held back, but there's a donation button). Admittedly I don't know how actively it is being maintained; I opened it for the first time in years and updated, but the update says it requires OS X 10.9, at least. Still seems to be running nicely on macOS 10.13.4.
I suppose the way I envision you using this would be to create PAR files from groupings of your photos, and then every year or so, checksum your files to ensure that the files are still pristine.
A number of people have suggested RAID and network backup solutions. The problem with those solutions is that all of them will copy a file, but they won't know if the file itself has become corrupted. The only way to know would be for you to check, yourself (which won't always be apparent), or to have a checksum of the original generated. PAR files don't just allow you to detect corruption, but to repair it. They're pretty useful.