what's the procedure to use if i have an images from unknown sources which i wish to use in wikiversity?

is it simply no go?

or are there particular conditions under which it may be appropriate - i seem to sometimes see images on wikipedia which are tagged to indicate that there is no other option except to use that particular image - how does this work?

feel free to point me to reading - i just want to get clear guidelines in my head

i don't have any specific images in mind - each year i rework teaching materials, i remove a few more proprietary images and add a few more free images, but it is a gradual process to eventually get everything fully free