I really hate these aphantasia questions. It feels too subjective. I can visualize in a sense, but I would never talk of an image. In fact closing my eyes makes it harder for me to imagine anything. I can recall my dream from last night for example, I can describe it quite well. If you now would ask me to in my mind modify for example the color of the floor, I couldn’t. Because in “dream reality” I very much remember…
One way to measure scientifically is to ask somebody to picture a room. The the experimenter keeps describing adding items to the room until the experimentee can no longer recall. By defining positions for all these items one could verify it is indeed visual memory by asking location questions.
I don't know if other people have thought of this and started doing it yet, but they should.