May 9, 2011 16:30 GMT  ·  By

Google has introduced an interesting new feature to its Image Search, the ability to sort images by subject rather than relevance. This makes it easier to find images even if you don't know exactly how to search for them.

"When you’re searching for images, sometimes it can be hard to come up with exactly the right words to describe what you have in mind," Donald Tanguay, from the Google Images team, wrote.

"For example, when you think of London, you might picture the iconic clock tower or the big Ferris wheel," he wrote.

"To make it easier for you to find images in situations like these, you can now use Google Images with sorting," he announced.

"Click on 'Sort by subject' in the left-hand panel and you’ll see images organized into categories that will narrow down your search and help you find the exact image of London that you want," he explained.

With 'Sort by subject' images are ranked according to the most popular ones, grouped by what they have in common. In Google's example, the most popular subjects related to London are the London Eye, Big Ben, London Bridge and the city at night.

This type of sorting makes a lot of sense for image search, since even if you know what something looks like you may not know what it's called. With Sort by subject, you can enter a general query and then narrow it down visually. Google lists a couple of perfect examples of this, types of flowers or dog breeds.

The new sorting feature is based, in part, on previous technology, such as Similar Images and the experimental Image Swirl. It's also a perfect example of how structured data can make web search better.

In this case, Google relies on several clues which indicate a relationship, from a similitude in the images to their context in web pages. The feature is now being rolled out for Google.com and the localized search engines and will be available for all over the next week.