First of all, well done on the successful upgrade. I know it's been a long time coming.
Since joining this board back in its Alpha days, I've collected over a thousand wallpapers that my OS cycles through on a random basis. Quite often, I do find myself looking up old wallpapers I've saved previously to see who the uploader was or remind myself who or what the subject of the wallpaper is from their tags. That was simple enough to do when I could rely on the wallpaper's numerical based filename to determine its URL.
Doing this would also have the added benefit of ensuring that the upgraded site does not take a massive hit in SEO rankings.
If that's not feasible, then is there any way for us as users to translate an old ID "775318" to its new hash/ID of "dgegxl" ourselves?