Is there a way to delete duplicate photos without deleting the original?
Of course! Deleting duplicate photos will not delete the original, particularly when they have the same name, e.g. "IMG_0001" and "IMG_0001 (1)" or "IMG_0001 copy". It's very safe, but if you have doubts maybe copy everything to a different folder in your Desktop first, just in case!
As far as I know yes. Of course if you have Dropbox synched to your computer, you can use search tools to help you identify the duplicates (search for "copy" or "(2)").
