Sorry to hear of your predicament. We hope things will improve for you in the job market and in general
Yes, you can store images in DEVONthink though if you need to keep track of image specific metadata, that’s not really built into our application. If you need real digital asset management, you’d be looking at an application like Extensis Portfolio, Adobe Bridge, Canto Cumulus, etc.
Is there any risk of image degradation?
I’m thinking things like auto compression
Enabling the record lock might add some protection
Other than that, I think Devonthink is an excellent tool for storage/organization of the collection
(I have no interest in going full DAM)
In answer to the op’s “To keep track of what I have download … access them from within Devonthink”