Step 1: Syncing
First of all, you’ll need to ensure your Facebook account is set up. Choose iPhoto from the menubar and click Preferences. Choose the Accounts tab from the top of the window, hit the ‘+’ sign and log in.
Step 2: Comment away
In the sidebar, a new Facebook option will appear. Click it to see all of your images from Facebook, then choose an individual album and photo. Click Info, then click below the comments to add your own.