The Terminal command posted previously didn't work for me, unfortunately.
But I figured out another simple solution, that doesn't actually turn off Faces,
but that does stop the annoying "Unnamed" bubbles from popping up all over your photos - which is all I needed:
1. Close iPhoto, then right-Click "iPhoto" app icon and "Show Package Contents"
2. Browse to "Contents/Resources" and look for the following files:
face-tag-BG.tiff
face-tag-BG@2x.tiff
face-tag-clear-N.tiff
face-tag-clear-N@2x.tiff
face-tag-clear-P.tiff
face-tag-clear-P@2x.tiff
face-tag-textField.tiff
face-tag-textField@2x.tiff
(The "face-tag" files are the individual parts that make up the annoying "Unnamed" Tags/Bubbles which are overlayed on your pics.)
3. Make a Backup copy of these files in case anything goes wrong:
Hold "Alt" while dragging the files to a new folder on your Desktop (Call it "Original Files" or similar...).
4. Duplicate the folder you just created and name it "Modified Files"
5. In "Modified Files", open each of the TIFF files individually in the "Preview" App (Strangely, Photoshop didn't work for me)
6. In Preview, for each file:
- Select all (CMD-A)
- Press "Delete" to delete the graphics
- Save (CMD-S)
7. Copy the modified files back into the iPhoto "Contents/Resources" folder where they came from.
You wil be asked to enter your Admin-Password for this.
8. Open iPhoto,then open any Photo with a face (or a group photo) and see it in it's full glory, without Face-Tags overlayed on the pic.
(If anything went wrong, just close iPhoto and copy the files from your "Original Files" folder back into Contents/Resources.)
Basically iPhoto still continues to do what it did before, but as all the "Face-Tag" graphics are empty now, you won't see any of it.
I've been annoyed by this for over a year (especially when looking at a group or party photo) and just signed up here to post this, so I hope this helps others as well!
(No guarantee if anything goes wrong!!)