Zilla is a free photo/video backup assistant that helps you to keep your memories backed up to your Flickr account.
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In order to mark a Flickr photo as a favorite, first, login to your Flickr account using your Flickr username and Flickr password and then follow the process mentioned. While viewing a photo, simply click the 'Favorite' icon i.e. the 'star' icon and the photo will be added to your favorites.