Mac OS X 10.4 and later include an option that allows you to send a picture to iPhoto using the PDF workflow feature of the print dialog. You can access this feature by selecting "Send PDF to iPhoto" from the PDF menu in the print dialog.
This feature uses an Automator workflow to create a PDF printout, and then convert that PDF to a JPEG. The JPEG is then sent to iPhoto. This workflow is installed by Mac OS X and is stored in /Library/PDF Services/.
Some important notes about this feature:
To learn more about creating your own PDF workflows, visit the AppleScript and Automator sections of the Apple website: