When you search for Pablo Picasso in google images your search returns many different results. Portraits of the artist, by the artist, and even related to the artist can be returned as search results. The same is true if you search google images for apple. Do you mean the fruit or the computer. Do you want the image in color or black and white, a straight shot or one from afar.
Image Swirl...in development in Google labs addresses this issue by displaying results in a cluster like way...you select what you like and it produces more similiar results.