The case, filed in a New York federal court on July 30, includes claims Zillow is using watermarked images owned by CoStar Group — parent company of competing home search site Homes.com — on its sites and on Redfin and Realtor.com through its rental listings syndication deals.

CoStar claims Zillow published more than 46,000 of CoStar's copyrighted photographs on Zillow.com and partner sites.

The chief executive of CoStar Group, which owns Apartments.com, said Zillow has ‘stolen’ thousands of images to bolster its business.