Google’s head of search spam, Matt Cutts, said in a recent video that using stock images from a stock image website has no impact on rankings.
The question was, “Does using stock photos on your pages have a negative effect on rankings?”
Matt’s answer was very short, he said “no.” There is no positive or negative impact on your organic Web ranking if you use stock imagery versus original imagery.
Of course, if you want to go deeper, images might enhance your content, which may attract more visitors and more links. But, images are currently not a ranking factor for your content, according to Matt Cutts.
Another obvious point is that this is not discussing image search ranking. Typically, you won’t see the same image shown in the image search results. So, having unique images may help there.
Here is the video from Matt: