The default setting on Flickr continues to be All Rights Reserved, but you can change the default for all your photos in your account settings if you’re interested in using Public Domain or CC0. You can also set the designation per individual photo in a variety of Flickr desktop and mobile experiences, such as the Photo Page, Camera Roll, Organizr, Uploadr, etc.Creative Commons has explainers on what it means to be in the public domain and CC0 or "no rights reserved" copyrighting. There are other licenses that give others the ability to make use of your work for non-commercial reasons or even to make commercial use of your work, provided they've built something else out of it.
|Screenshot of creativecommons.org. Everything on the site is|
copyrighted but under a creative commons non-commercial
and with attribution use license.
|I cheated and ended up searching "GenCon." Photo credit: Mass Effect Costumes|
at GenCon, (c) Benny Mazur, available on flickr.