Looking for iPhoto 8 compatible iPhoto diet to pare down "runaway" duplicate JPEGS. I have thousands of photos and don't know what to do--all in a single library. Really isn't practical to do it manually.

Pic thumbnails in iPhoto 8 have duplicated titles, e.g., P6260008.JPG but the thumbnail image is actually missing showing dotted outline only if using >4 thumbnails per row (5 or more across reveals the thumbnail image!) . File size shows the image exists. For the imediately adjacent thumbnail, the root title shows up, sans the '.JPG' suffix, along with a normal [visible] thumbnail. Double clicking this one brings up the full image, as it should. Double clicking the former, i.e., missing thumbnail (dotted line shows up) brings up only a blurry exclamation point in a circle.

I don't get it. Afraid of doing damage to data. Suggestions?