By adding a Creative Commons license to your photo, you can allow others to share it or re-work it, as long as they give you proper attribution.
The Flickr team had this to say:
We are proud to announce that – thanks to you – we now have 200 Million (and counting) public Creative Commons licensed photos on Flickr. This makes us the largest CC photo repository in the world!
You can browse and search those CC photos by license, or find exactly the one suitable for and available to you. by using advanced search, ticking the CC checkbox, and searching for whatevery image you are looking for.
If you would like to take part in CC and provide your photography under a less restrictive license than “All Rights Reserved”, familiarize yourself with Creative Commons, and apply a CC license to you photos, by either changing your default license upload setting or an individual photo’s license under “Owner settings” on any of your photo pages.
Flickr is clearly one of the most attractive pieces that Microsoft is looking to pick up in their potential bid to acquire Yahoo! That is a story that we’re watching closely. Also, other larger photo hosting and sharing services including Facebook don’t allow you to offer your photos with a Creative Commons license, so this announcement doesn’t make Flickr largest host of photos in the world.