Facebook is certainly one of the largest photo-sharing websites in the world.
With new upgrades to it's photo component such as high resolution images, photo download links, multi-tagging capabilities and a helpful lightbox interface for image browsing, Facebook is certainly striking at the heart of Flickr's core constituency.
The hi-res image feature to the website will allow sharing of print-quality images, which may also introduce new potential revenue streams in the future.
The image lightbox feature will contain the tagging system, a comments gallery and advertisements.