I couldn't find this information, so thought it may be a useful addition for Help.
1. Click on the photo you want to move.
2. Scroll down to list box under 'People & Things in the Image:' and check the box by the target profile for the image.
3. Click on the 'SAVE CHANGES TO IMAGE DETAILS' box.
This will add the profile to the list at the top of the 'People & Things in the Image:' section.
4. From that list, select the profile you want to move the image from and click the 'REMOVE from image' button.
NOTE: Don't remove the image before you add it to the second profile. I haven't managed to find one image removed before I added it to another profile.