I don't know how it is in US but here in Europe you would keep neither oil nor acrylic painting behind glass. You keep paper paintings behind glass (like watercolours etc.) but you don't paint oil on paper.

The fact that on your photo the painting IS kept behind glass, I think it indicates one of two things, the second one being really interesting:
1. either this is not the original
2. or the original was first painted with oil or acrylic and the photoed or scanned and then messed with some more in Photoshop or whatever and then printed on regular paper. And then put behind the glass for savekeeping