I loaded a bunch of images (from Dropbox) into the Binder. All good so far. Then I edited a number of them, deleted them from the binder, and re-loaded them by dragging them in from the Finder. The new files had exactly the same names as the old ones, but they were slightly different versions (cropped, rotated, etc.).
The result is that now when I go to embed an image in the text using Insert=>Image Linked to Document, the list of images contains multiple entries for each file. In other words, the internal database that Scrivener apparently uses seems to be holding onto the old images, despite them being removed from the Binder. The attached image shows the problem: there should be ONE of each image.