Flickr is a photo sharing website which allows you to post your own photos, comment on photos, and search for images with a Creative Commons license.

Flickr Commons allows you to search Creative Commons photos only.
Choose your Creative Commons license

How to get the most out of Flickr
Tips for Flickr beginners
How to upload your photos onto Flickr
Flickr Organizr is great for organising your Flickr photos

Finding and using Creative Commons images on Flickr