Flikr started out as one of numerous websites that allowed people to post their photos to the web and share them with other people so that you didn't have to mail [email or snail] them to grandma or your mom.
Today, Flikr is a social media site that allows people and organizations to share their digital photos with others around the world by incorporating tagging, geotagging, and Creative Commons licenses so that they can legally be viewed, shared, and often-times used by people miles and countries away. Flikr also allows people to join together in groups, like the Libraries and Librarians group to share content, information, and expertise.
Flikr is widely used not only by people but by organizations, which is part of what makes the site so spiffy. I now know what a CIA library or Grand Duke Carl Francis, the Emperor of Austria look like thanks to the CIA and the Library of Congress, respectively [both images are in the public domain]. I can also look at content posted by the American Library Association who have posted some fun little bits about the ALA Annual Conference that recently happened in New Orleans.
Many of the wonderful organizations that are on Flikr participate in The Commons which is one of the largest public photography archive. The Commons includes photographs of famous and not-so-famous people and places from around the world. These images are all part of the public domain and can be used, linked to, and such by anyone.
Beyond The Commons, Flikr also encourages the use of Creative Commons licenses so that photographs published to the site can be used in various ways legally. Many photographs are published under a simple Attribution license so that as long as the original creator is given credit for the photo, you can do with the photo what you like.
The Commons, and the photographs released under Creative Commons licenses on Flikr, are what makes the site so useful to those teaching information literacy. We know that people search the web for content to use and share with others. We have an obligation to teach people how to do so legally and freely. Flikr, and sites like it, allow us to do this easily as we can show people how to search for images they can use, as well as show them how to cite creators of content.
As a side note, two other great resources for content that can legally and freely be used by others are the Creative Commons search engine and the Wikimedia Commons.