I don't use Bing myself. I agree with baniels on how the searches come up.
Last year La Jolla hosted the Cow Parade (local artists paint plastic cows for charity) and we took our cat Posey when we saw them. Doing a search on Bing using Posey Cow Parade, the second entry is from Flickr, but my photostream, not the set of the Cow Parade. Doing the same in Google, the 3rd entry is a photo from that set.