Every level of Creative Commons (cc) license requires that you attribute the photo back to its original source.
Flickr Community guidelines offer guidance as to what such attribution must include:
Do link back to Flickr when you post your Flickr content elsewhere. Flickr makes it possible to post content hosted on Flickr to other web sites. However, pages on other web sites that display content hosted on flickr.com must provide a link from each photo or video back to its page on Flickr. This provides a way to get more information about the content and the photographer.
It’s a good idea to go a little further than simply linking back to the Flickr photo, though. As a general rule, you should provide the title of the photo and it’s author, and that information should be available someplace fairly close to where you put the photo.
Another option is to add that information into the caption for the photo (see illustration to the right, which shows the media manager dialog box, with that text entered in the caption box).
Note that sometimes photographers post specific instructions on their photos about how they want their work to be attributed. If they do, you should follow their individual request.
That second option will look something like this when you insert the photo into your page: