Im not sure how others work with their moderators and super moderators, but for moderators I allow them access to the Super Moderator Control Panel, then for Super Mods I give them a small part of the Admin CP.
To change the settings for that you go to Admin CP - Usergroups - Moderators and edit the settings.. Scroll down till you see something that looks like this:
It says both Admin CP and Super Moderator CP, click the SM box and they will be allowed to see all images including private images.
Please do correct me if I am wrong.