1. A computer-implemented method for image retrieval using a statistical bigram correlation model, the method comprising: receiving a plurality of images responsive to multiple search sessions; determining whether the images are semantically relevant images via relevance feedback; and estimating a respective semantic correlation between each of at least one pair of the images with a respective bigram frequency, each respective bigram frequency being based on multiple search sessions in which each image of the pair is indicated to be a semantically relevant image.