[caption id="attachment_13461" align="aligncenter" width="618"] Google's homepage: ad-free, but for how much longer?[/caption] Violating a self-imposed ban on cluttering its search-results pages with garish advertisements, Google has begun testing full-sized banner ads. The ads are linked to certain keywords, such as Southwest Airlines, although they don’t appear every time the appropriate terms are inputted into the search bar. Google claims the effort is an experiment. "We're currently running a very limited, U.S.-only test, in which advertisers can include an image as part of the search ads that show in response to certain branded queries," a company spokesperson wrote in an email to ComputerWorld. "Advertisers have long been able to add informative visual elements to their search ads, with features like Media Ads, Product Listing Ads and Image Extensions." Test or no, the presence of colorful ads in Google’s search results goes against the company’s very public vow, made in late 2005, to never include such things. “There will be no banner ads on the Google homepage or web search results pages,” a company executive wrote in a corporate blog posting at the time. “There will not be crazy, flashy, graphical doodads flying and popping up all over the Google site. Ever.” The Google executive who signed her name to that posting? Marissa Mayer, who’s now CEO of Yahoo. If Google decides to expand this banner-ad experiment into a full-fledged effort, it would be a sure sign that the company is on a determined hunt for new revenue streams. Although Google offers a variety of products—everything from email and apps to operating systems for mobile devices and PCs—it still depends on advertising revenue to fuel an overwhelming percentage of its bottom line. And while Google dominates the market for desktop search, it faces a number of determined competitors for mobile-advertising dollars, including Facebook and Twitter. As more people make mobile devices the center of their computing lives, that increases the pressure on Google to do something—anything—to expand its advertising footprint. But whether banner ads and “graphical doodads” would prove acceptable to customers accustomed to Google’s minimalist blue-link ads, well, that’s another question entirely.   Image: Google