Are you using stock photos or images in your website? Recently Matt Cutts (An Google Official) discussed this issue.
According to him Google is not considering the use of stock images as a negative factor for ranking. It means that if your website is using these images then your ranking may not be hurt. The websites with original images and websites with stock images will be ranking same if all other ranking factors are same.
All this sounds good to many of us. But he also shared more thoughts. For instance he told that currently this is not the ranking factor but we cannot say that this will be the case in coming months or years. May be in near future we may rank websites higher who are making efforts to produce original and unique images as compared to those websites who are using stock images that are used and re used by many websites.