In reply to The Lemming:
If your Duplicate photos are spread across many Folders -
Search the entire computer for all images of a particular format, I.e. Jpeg ect
Change the view settings so you can see a thumbnail of the pictures
Manually identify which photos are duplicates, and then delete.
If your Duplicate photos are contained within One folder-
Sort by date/time taken then Identify which images were taken at exactly the same time, confirm they are duplicates and then delete.
Or get some fancy image recognition software.