(This is an answer we gave at a recent editorial workshop, repeated here for anyone who missed it).
The best way to attribute images is a simple line of text at the bottom of an article that says:
- Photo above by John Smith on Flickr. Used under Creative Commons.
Link to the original photo with the John Smith bit and link to this licence http://creativecommons.org/licenses/by-nc-nd/3.0/ with the words Creative Commons.
If possible, drop the person a line to check if it’s OK.
Be careful if it’s a sensitive issue that may cause offence. Use common sense.
Putting it in an alt tag isn’t good enough. If you need to attribute a photo on your department home page then put the attribution at the bottom of the content item that the image is associated with (It isn’t possible to put text attribution on department home pages at the moment).