Okay... Works, after a fashion.
When I drag an image from a Chrome tab with the folder into the tiddler containing your macro, I get
<code>./Graphics%20Samples/</code>
before the filename and no image shows in the Tiddler (this is NOT part of the file path to the image).
But once I delete the above addition, all works fine :)
It still adds the '%20' in place of spaces in the filename, but they can safely be replaced by spaces (if I could write filters, I could probably add one to automatically convert them back to spaces, but...)
In any event, this will still be quite useful - Thank You, Charlie :)