Flickr
From CollabWiki
[edit] What is flickr?
flickr allows for sharing, tagging, geotagging, grouping and searching of images. In other words, say that you’re looking for an image - say of “Pakistan” or something more abstract like “colorful” – if you go to flickr.com and enter word(s) in the “Search” field, like “Pakistan” or “colorful” or even both, then it will return all photos with those tags/text. This can be done without having to register with flickr or without having to log in.
Moreover, say you want to use a photo for your own purposes. Most images on the web are copyrighted so that you are not really allowed to use them. In flickr, you can look up photos that you are allowed to use (that fall under the Creative Commons license, in which the owner of an image licenses it in such a way that others can use it).
For example, if you do an advanced search on “Pakistan”, you can scroll down to “Only search within Creative Commons-licensed content” and check that box to get search results of images that you can re-use.
You can also add comments to particular areas in an image. Check out this photo -- when you mouse over the image, you'll see the areas which people have drawn and commented.
Note also that it's a photo that falls under the Creative Commons license, so the image owner has ok'd it to be used. (scroll down under the "Tags" section to where it says "Additional Information" - you'll see it says "Some rights reserved" which indicates that you can share and remix the work as long as you attribute ownership to the original owner and it's noncommercial).
Note also that above the image, there is an "All Sizes" button which allows you to download the image in several different sizes (thumbnail, small, medium, large).
If you wish to share your flickr pics on facebook, there are a plethora of facebook apps that allow for easy flickr-to-facebook sharing, such as My Flickr, which allows display of one's photos according to certain criteria such as: Recent Photos, Tags, Interesting, Date Range, Photosets, etc. and flickr facebook.
So, flickr has become a huge shared database. One interesting project is the Flickr Commons project - which consists of a wealth of old Library of Congress photos and an invitation to collectively tag them, thus enriching the image collection as it grows with our collective knowledge and imbued meanings.

