Terminal makes life easier, consider it like knowing how to wire a plug - 240 Volts at 13 Amps will kill you quickly but if you unplug and take sensible precautions rewiring is simple.
Drag & drop to autofill the file paths in Terminal. CTRL + C will stop any running command or clear the current typed text.
'sudo' will need to be used inside an admin account, it gives system level (e.g. root) access. Backup first, remove any disks if you are paranoid.
You can try the commands without sudo first but I expect that will fail with permission denied or 'operation not permitted' errors.
This will try to strip all ACL's recursively…
sudo chmod -R -N /path/to/iPhotoLibrary
Add the ability for the group to read & write, I'm assuming the group is set to staff, which all users should belong to by default.
sudo chmod g+w -R /path/to/iPhotoLibrary
If the group isn't staff change it…
sudo chgrp -R staff /path/to/iPhotoLibrary
You will also need to look at any enclosing folders, the staff group will need read write too.
You can set the POSIX permissions in the GUI via get info, ACL's may have been added to the get info dialog (I'm not on 10.8), but that is a PITA for thousands of files nested inside hundreds of folders. - Try the 'propagate to enclosed items' - option if you like. I haven't seen that work very often, it is lazy about giving you full access.
You may want to see if anyone has any better ideas, there must be a GUI app to fix permissions on 10.8 but I find Terminal is usually quicker & more powerful.
BatChmod could work, but I haven't used it for many years.
http://lagentesoft.com/batchmod/index.html
Re:co