On asking a question, "Does using stock photos on your pages have a negative effect on rankings?", head of Google Search Spam, Matt Cutts said, it doesn't impact the ranking.
Cutts in the latest Webmaster video said that stock images from a stock image website has no positive or negative impact on the organic Web ranking, if you compare stock imagery with original imagery.
He added that images might enhance your content & attract more links and visitors. But, at present, Google doesn't consider images as the ranking factor for the content.
Matt Cutts however said that considering the quality of the photos is a great suggestion, which Google might look at in terms of search quality. So, there are chances that websites with original images might rank higher than the ones using stock photos over and over again, in future. But, at present, there’s as such no ranking criterion on the basis of images.Matt Cutts on the Impact of Stock Images on Search Engine Rankings!,