iPhoto albums are great for sharing with others. If if you don't want prying eyes to have unwanted access to your images, you can protect your shared albums with a password. This amounts to "locking" the iPhoto album in the "Preferences" pane. You can lock or share individual photos or full albums.
Click the iPhoto icon in your dock to launch the program.
Select "iPhoto" from the menu, then scroll to "Preferences."
Click the "Sharing" tab in the toolbar.
Check the box next to "Share My Photos." Choose to share your entire library, or select certain albums by clicking the radial button next to your preference.
Check the box next to "Require password," and type your password in the text box.