Identifying images that have been scanned

My photo collection includes some old family photos that were scanned in over the last few years. I'm trying to seperate them out from my regular photos because they all need fixing up.

I was hoping to create an album easily by selecting everything that doesn't have a camera metatag. But there doesn't seem to be a way of doing that. Filters can select one camera metatag but not a blank/missing tag. Smart album rules are the same. The only option is 'include' and one value.

Any suggestion for how to achieve it?