Have you uploaded images to Flickr? Have you set some of the images to be creative commons licensed images? Flickr has announced plans to start selling the catalogue of 50 million Creative Commons-licensed images, without a penny of the profit going to the photographers that took these images. Much like when Instagram committed social suicide by allowing your images to be used in ads, you should have seen this coming. Over 300 million Flickr images come under the Creative Commons license, and the agreement you dear user made with Flickr allows them to sell your CC images for profit.
Now, I'm not a lawyer, but I play one on this site. Just apply logic to this scenario: Can you change a copyright license to be more restrictive after you've had it 'free for all', for a period of time? Wouldn't that set "legal traps" for people, they use it according to one license for a while, and then you change it later, only to try and sue them? Whether it is legally binding after the fact is probably a matter for the courts, in the many jurisdictions we're playing in, as Flickr actually allows you to change to a more restrictive license after using a very open CC one. And there's no public logs of when a license may or may not have changed, and discussions on Flickr says that they have no history of license, not even for their own internal investigation. So while I think it's legally illogical to be able to change a license after the fact, and apply a much stricter one instead, there's seemingly nothing stopping you. Except this:
CC licenses are not revocable. Once something has been published under a CC license, licensees may continue using it according to the license terms for the duration of applicable copyright and similar rights. As a licensor, you may stop distributing under the CC license at any time, but anyone who has access to a copy of the material may continue to redistribute it under the CC license terms. While you cannot revoke the license, CC licenses do provide a mechanism for licensors to ask that others using their material remove the attribution information. You should think carefully before choosing a Creative Commons license.
The news about this will probably have many people changing their licenses, or at the very least optioning to not select Creative Commons with the next batch uploaded. It'll be very interesting to see how Flickr will deal with that.