Know how to Use Creative Commons Images from Flickr
Flickr is an excellent place to find images that are available under a Creative Commons License but it won't let you properly attribute CC work.
Some Creative Commons images are licensed as "Attribution Non-Commercial" and thus they may not be used on websites that, say, carry advertising. For more, see this PDF report on defining non-commercial use.
Searching Creative Commons Images on Flickr
Flickr has a dedicated page to help you easily find images that are available under Creative Commons. Or you may use alternative tools like Flickr CC, Flickr Storm and Comp Fight that are in some ways better than Flickr's own search interface.
Using Creative Commons Images from Flickr
If you are using an image from Flickr, all they require is that the image on the external site should link back to Flickr's page where that image is originally hosted.
The problem is that Flickr's current style of attribution doesn't meet the Creative Commons guidelines for attribution which require that you:
Cite the author's screen name (link to the author's profile page).
Cite the work's title or name (link the name directly to the original work).
Cite the specific CC license the work is under (link to the license on the CC website).
The HTML code that Flickr provides for embedding Creative Commons images on to other sites satisfies only one of the three guidelines for attribution.
You can however use an online tool called ImageCodr
to generate embed code that meets all the attribution guidelines of Creative Commons as well as Flickr. Just put the URL of any Flickr image into this tool and you get a code that satisfies all the requirements.