Split document library

Hi

Why not create a new site collection with a new library. Create your new information architecture in this new environment. You can test your new way of working here.

Then I would use a tool (perhaps ShareGate) to migrate the content to the new environment.

[edit] ...and once the migration is succesfull delete/backup your original content ;-) [/edit]

Please think your new information architecture (your folder structure as you suggest) through. Perhaps you did this already but just didn't mention because it was a bit off-topic.

Then I would suggest another tip.

Perhaps you can use cognitive services to auto tag the images for you! I've been googling a bit for an example and found this link:

https://gunnarpeipman.com/sharepoint/sharepoint-describe-tag-pictures/

Another tip:

Who are your content users? How do they use these images? How do they find the correct images?

Who are your contributers? Who is actually uploading the images? How can you help THEM upload the images in such a way that the content users can find the images quicker? 

#hopethishelps!