Right clicking with my mouse didn't produce anything but after clicking on the photo in iPhoto I went to the iPhoto toolbar, and then over to File, and then down to Reveal in Finder, and then over to Original File. That opened another window with the photo to be deleted and any other photos in the album. I could drag that image down to the trashcan so I can use Secure Empty Trash. Then, return to the iPhoto window and the original image, highlight it, and choose the trash can.
I'd be willing to bet a power user could point out a method using about two key strokes that would accomplish the above. Kind of a PITA using my method.