Here is the modification that Chuck provided to not show duplicate pics in the thumbnail preview filmstrip:
In showphoto.php (version 5.31) replace lines 250-319 with this block: (I hope I've got this right Chuck - please correct me if I am wrong - this seems to work fine for us)
Content visible to verified customers only.
Is there any way to prevent duplicate copied pics in: Most Recent 1 day 7days 14 days All Images
showgallery thumbnails display?