I read somewhere one way to prove it is a scan of the album. What would that mean? If I took a picture of an album, would that be considered proof?

Yes, it can be something like that you can show us. But not just a mere CD-R.

Scans and photos are both good ways of proving a release's physical existence. Photos are easier a lot of times because you can capture the full packaging. I had to do it here:
http://www.metal-archives.com/release.php?id=210841

Scans can be used a lot of times for reviews in magazines that can't be found on the internet or things of the like.

By the way, just because you proved that a release exists doesn't mean that you've proved metalness. Make sure you have samples ready for the mods too.