I rename/caption media according to its collection. A census image would be named/captioned as "1940 US Federal Census - North Dakota, Mountrail, Sikes, 31-47, Image 5". If the image is linjed to only one person, like military records, they get the person's name, last then first/middle appended after the collection name.
If I get a better copy of an image, I give it the same name as the file I want to replace and add a letter "a" right before the file extension. Then I move/copy it directly to the media folder, delete the old copy (without the "a") then remove the "a". FTM doesn't know the difference and all links to the file are intact.