At present search engines rank images based on the presence of keywords in text associated with the image, rather than the image itself. Results are often unsatisfactory and inappropriate. Image analysis results remain poor in spite of decades of research in the field.

The New York Times reports that search geniuses intend to introduce a system for image searches that is similar to PageRank, which is used for Web search. The new PageRank for product image search, or ‘Visual Rank’ as it is called, will actually try to understand the picture or analyze the visual link structure.

Image recognition, which is expensive and time consuming, usually breaks down with any images other than faces, alphanumeric characters and very specific objects. The new technology will instead try to identify more objects and also perform a link analysis with image processing. In this system, a numerical weight will be allotted to all images, thus weighing its relative importance vis-à-vis other images.

Classical image recognition methods can only compare images with a known image. However, with VisualRank, Google will use “visual themes”, to rank each image from a given set of images, based on how well it matches the theme. For example, when the word McDonald’s is used, the algorithm would identify the famous golden arches from their logo as the theme. A picture where the arches are prominently displayed would then be ranked higher than one in which the arches are in the background.

During a recent study Baluja, Jing and 150 panelists surveyed 2,000 of the most popular products search on Google. It was found that the VisualRank algorithm reduced irrelevant results by 83%. As of now all this has been done only on an experimental level and it remains to be seen whther Google can scale the technology and apply it to their entire database of images.

In an email to Search Engine Journal editors, Matt Cutts said, “The partial update to visible PageRank that went out a few days ago was primarily regarding PageRank selling and the forward links of sites. So paid links that pass PageRank would affect our opinion of a site. Going forward, I expect that Google will be looking at additional sites that appear to be buying or selling PageRank.”

Sites affected by this update included Forbes, the Washington Post, Search Engine Roundtable and Search Engine Journal, all of whose PR fell to 4, SF Gate and Sun Times whose PR has fallen to 5 and TechCrunch and Engadget whose PR was reported to have fallen to 5 but is now back to 7.

Changes in the PageRank do not seem to have affected traffic to any of these sites though. This may change over time if Google decides to punish the sites for selling links. However, for now it seems that the PageRank update was only meant to remove their ability to sell high PR links by simply dropping that number.