Memories are less vivacious than 'perceptual' images, for example. This is not quite an answer, yet. The step open seems to be to say that when I have had a 'perceptual' image, and careful investigation has revealed that it was a 'perceptual' image, I remember what it was like. Next time I have an image I can then classify it. Hume's putative solution comes under a general class of 'label solutions'.
Different images have different identifying characteristics, or 'labels'.
All I have to do to identify what sort of image I have before my mind is to remember which label goes with which image. Until the mid-twentieth century most philosophy of mind involved an account of differentiation between images which had labels of some sort. But, according to the empiricist philosophers I have just mentioned, remembering also involves images. In fact a memory is one sort of image. But memory is sometimes mistaken, as we have seen.