Registering an account is optional however it has various benefits:
Registering your account is the best way to save your favorite photos into a list. If you ever have to add more photos to your favorites list or remove or organize your photos, Registering your account makes it easy for you. Without that, you may loose your favorites list once you close your browser session and will have to redo everything.
Additional benefit of Registering an account is that you can create multiple favorite lists if you have to share different photos to different friends.
