Adding the other sense and even a history, does a lot to support the “realness” of the image. Without this, they become kind of washed out and prone to fading. Of course, you can concentrate all your efforts on the visual image but it at a certain point it might be more efficient to add a smell or other kinds of information.
When you recall actual images from your past they come with a lot of sensory and supporting data. You may not be noticing it but it gives it that credibility.
In real life if you encountered something that had no smell or sound, your brain might tell you this is a hallucination. Reality is rich in detail. Everything comes with a history, a social context and emotions.
Walk into the room. Smell it. Run your hands over the walls. Carve your name on the wall. It’s old heavy wallpaper and wants to tear. A small insect scurries away. A friend of yours used to live here and he made curries when you came over. The odor still lingers. He had a favorite song and you hear it now. It always made you laugh when you heard it. You remember now, helping him move in and out. You are still safekeeping his guitar. Dig a hole in the floor. Taste a piece. It’s chicken vindaloo!. Turn the light on and off. OMG! There’s a toilet in the corner!! A working toilet! But it’s pale green, the same as the walls so you didn’t see it at first.That’s just crazy! Piss in it. Flush it…
Try it on for size. I suggest that if you spend some time in that little story above. You will have a very persistent, real feeling image. I suspect that you will remember it for while without further effort.
It helps to be a little crazy.