Despite several efforts, actual image search that can effectively analyze and compare objects on an image remains very limited today. Google's new research effort dubbed 'VisualRank' combines image-recognition software methods with ranking and weighting techniques like the ones used in PageRank to compare similar objects. The search giant said it tested the algorithm using Google's product search 2000 most popular queries like Wii, Xbox and iPod, and the image results were about 83 better or "less irrelevant."
As you are probably aware, current image search provided by Google or Yahoo rely on a page's text for indexing, which usually works about fine for searching using a string of text. This new initiative could open the doors for image vs. image type of search.