That image is part of the Finance contest that it currently held at HubPages. See http://hubpages.com/money for more details.
I don't think the image is in public domain but I also don't think they have stated any license. In any case, it's rather free to use that image because anyone can write a hub using that image. However, when the contest is over it might not be appropriate to use the image because it is related to the contest.