I scanned old photos as 16 bit gray scale with Epson Scan on my V700.
The looked fine in Preview, but in iPhoto '08 (most recent) they had black previews and oddly inverted and faint views.
This has been a probelm since version 5.0.4: iPhoto 5.0.4 or later: Grayscale images appear inverted.
The scanner inserts a color profile, and they're not color images. iPhoto gets confused.
One would think that over 3 versions Apple would have come up with better iPhoto behavior.
I removed the color profiles using the suggested AppleScript (see link) -- one at a time.
That worked. I'm sure there's a faster solution.
Very annoying, and it's only thanks to Google that it wasn't very aggravating.