I got a message" the iPhoto Library is a Time Machine back up, and so cannot be used as the main library. Reopen iPhoto with the Option key held down to choose another library." Does this mean my photos are backed up on my external drive?
Time Machine is not a 'normal' storage drive; it uses a unique file structure and can't be used to run iPhoto or anything else from.
Read Pondini's TM articles; http://pondini.org/TM/Home.html
Retrieving data ...