The suit, filed in U.S. District Court in the Southern District of New York, claims Zillow has displayed nearly 47,000 CoStar-copyrighted images on Zillow.com. CoStar is asking for permanent injunctive relief as well as “a substantial award of damages,” which could top $1 billion.

“Zillow’s theft of tens of thousands of CoStar Group’s copyrighted photographs is nothing short of outrageous,” Andy Florance, CoStar’s founder and CEO, said in a statement. “Zillow is profiting from decades of CoStar Group work and the billions of dollars we have invested. … We are committed to stopping this systematic infringement and holding the wrongdoers to account.”

Zillow, which was sued earlier this month for antitrust, did not immediately reply to Fortune‘s request for comment on the suit.

CoStar says it has, for decades, employed thousands of professional photographers to take pictures of residential and commercial real estate, licensing those photos to brokers, property owners and more. The photos, it says, are registered with the U.S. Copyright Office and watermarked.

Zillow, the company alleges, has been using those without paying for them. Rental listings seem to be at the heart of the complaint. Because many photos appear on multiple listings and pages, CoStar says they were displayed more than 250,000 times.

The suit also alleges the photos appear on Realtor.com and Redfin, which are owned by separate companies. CoStar accused Zillow of distributing the photos to those sites via a syndication agreement. (Neither of those sites is included in the suit, but Florance said “if these other sites do not immediately remove our images, we will have no choice but to sue them as well.”)

“Zillow has unlawfully published and used tens of thousands of CoStar’s copyrighted images to attempt to increase its standing in the online rental listings market,” the suit reads. “While Zillow may try to blame its customers, it is Zillow itself that is using CoStar’s images to build its products and earn revenue.”

CoStar has prevailed in this battle before. In 2019, it secured a $500 million judgment from the bankruptcy estate of Xceligent, a now-defunct real-estate listing platform, over the use of 38,489 copyrighted photos. The $1 billion estimate is drawn from the larger number of photos and appearances in the allegations.