I don't know if it's the same for mobile but CoC2 has two folders, one for full busts(the ones you see when you click on a portrait), and one for cropped busts(the ones you see on the right side)
a solution for this is to delete the "fulls" folder to half the file count, you won't be able to see the full sized images but most of the busts in the game will be alright. here's a screenshot for an example of what i am talking about.
as you can see you can cut down your image count by about half if you do that, but the thing is that the filesize won't change a lot since the compression algorithm the devs use is fairly good, could be useful for if you really want to save for all the extra space.
Edit: on a bit of an unrelated note, devs can't just use a single folder with the "full" busts because not all of them are centered and the whole "crops" folder centering is done by hand, that is just my guess.