The Internet titan on Wednesday reasoned that the small experiment is part of an ongoing evolution that has seen maps, pictures, telephone numbers and other "extensions" woven into advertising on search results pages.
"We're currently running a very limited, US-only test, in which advertisers can include an image as part of the search ads that show in response to certain branded queries," a Google spokesman said in an email response to an AFP inquiry.
"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."
A picture fired off at the Twitter account of digital marketing company Synrgy showed that a Google search targeting Southwest Airlines (NYSE: LUV - news) delivered results topped with a large ad showing a promotional photo accompanied by links for reservations or other services at the company.
Google is testing such large ads in collaboration with a limited number of brands and only in connection with Internet searches done on desktop or laptop computers, not on mobile devices.
"There will be no banner ads on the Google homepage of Web search results pages," Mayer said in a blog post that remained available online Wednesday.
"There will not be crazy, flashy, graphical doodads flying and popping up all over the Google site. Ever."