For example, in this album cover:
Is the text "imposed" over the image? What is the right word for placing one layer of design on top of another?
Text over an image.
Text on a background.
As Jenna answered, "overlay text" perhaps - not a term I'd use, but I'd have an idea about what someone meant if I heard it. "Overlay" to me, always infers opacity to a degree. Not the same thing in my mind as "text over an image".
I don't think there's a "special" term for it.