Jillaine,
I LUV this question! I, too, have thought it very strange that most graphic files on WikiTree don't have any data other than the default assigned name. You made me scratch my head a bit about what it would take to get people to enter data and I admit that most of my thoughts were sarcastic at best, with some that are not appropriate for the respectable grandmother that I like to think I am.
I finally did come up with an idea, though. There is no reason why the upload process can't include data fields, in addition to having the person select a file to shove across cyberspace.
Instead of assigning a default name, WikiTree could easily REQUIRE that a title be filled in on the same form as the file is selected for upload. If the title is blank when the form is submitted then an error message would appear instead of the file being accepted for upload.
While they could probably do the same for other data fields, that might not be a good idea to enforce all data being required. They could, however, encourage entry of that data by including fields for it on the upload form, even though they would accept the upload if they are left blank.
One other thing - the fields for the data (other than the name) are way down at the bottom of the page. I suspect that a lot of people don't ever scroll down that far even if they do any editing at all. Perhaps if they above the photo, it might help.