For small businesses and ecommerce marketers, that's one sizable audience -- a fact that hasn't been lost on the search giant.

Looking to better leverage the popularity of Google Images, the company today unveiled a new ad format and redesigned user interface for its image search page. The new features are rolling out to users this week and should be broadly available by week's end.

On the advertising side, the new format called Image Search Ads lets advertisers offer relevant image ads at the top of an image results page. For example, an image ad for a particular brand of sneaker might appear in the results page for the search "running shoes." Google previously offered only text ads on Images page.

'The changes to the ad program are significant because they will bring more engagement," Greg Sterling, contributing editor to Search Engine Land, told InternetNews.com.

The images site itself now features larger images, more information in bigger thumbnail previews and "infinite scrolling" that lets users scroll through -- rather than click through -- multiple pages to see more images. Google said a page can now hold up to a thousand images.

The improvement won't just help users find what they're looking for: Sterling said users who can't be troubled to click through multiple pages of search results would be exposed to more links with infinite scroll. That's potentially critical for the thousands of search marketers who rely on Images Search to turn up pictures of their products.

But Sterling also noted that Microsoft's Bing has already had the infinite scroll feature and has been touting the image display capabilities of its search engine.

Google vice president Marissa Mayer declined to answer questions about the competition in search features, except to say, "We are the image search leader -- the best in the world."

She also said that the infinite scroll feature is something the company would consider adding to its main Google.com search page.

"It has some potential, but the caching piece is difficult," she said. "With images, there is slightly less diversity and caching works better, but it's something to think about."

Features in the redesigned Google Images page include larger thumbnail previews and "Similar Images" search. Once you've selected a result, you can click Similar Images on the left column pane to get a set of image results that Google has identified as being similar. You can also further refine the results by clicking Similar Color -- for instance, narrowing down a search for "tulips" to display only yellow tulip images. There are other options, too, like the ability to search for line drawings.

Google Images product manager Nate Smith said the Similar Image feature is the result of sophisticated computer vision technology.

"Did you know there are nine subspecies of leopards, each with a distinct pattern of spots? Google Images can recognize the difference, returning just leopards of a particular subspecies," he said in a blog post.

Smith said some of the changes only took about a week of engineering time, "but it took a year to figure out the right way to do it."

The first beta of Google Images launched in 2001 with 250 million images. By 2005, the index had grown to a billion and today has grown to over ten billion images.

David Needle is the West Coast bureau chief at InternetNews.com, the news service of Internet.com, the network for technology professionals.

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