CoStar Group is suing Zillow Group for allegedly using tens of thousands of copyrighted real estate photographs without permission. The complaint was filed last week in the U.S. District Court for the Southern District of New York.

According to the lawsuit, CoStar accuses Zillow of publishing at least 46,979 images owned by CoStar across its rental listings platform. The company says the photos were used to encourage landlords and property managers to claim listings that were not necessarily available, after which Zillow sold them advertising services and promotional tools.

CoStar, based in Arlington, Virginia, operates several property listing sites, including Homes.com, Apartments.com, and LoopNet.com. It claims the disputed photos, many with visible watermarks, were also distributed by Zillow to other platforms through syndication agreements. Realtor.com and Redfin, which received some of the images, were reportedly asked by CoStar to remove them. Neither company has provided a statement.

Zillow has not responded publicly to the allegations.

The lawsuit states that CoStar licenses its images only to real estate professionals and does not authorize redistribution. It describes Zillow’s actions as widespread infringement and seeks compensatory and punitive damages, which it says could exceed $1 billion.

CoStar has previously taken legal action over similar issues. In 2019, it obtained a $500 million judgment against the estate of listing platform Xceligent after it published over 38,000 of CoStar’s copyrighted images. Xceligent had filed for liquidation two years earlier.

Zillow is also a defendant in another ongoing lawsuit filed by Compass in June. In that case, brought under federal antitrust law, it alleges Zillow attempted to gain control over private home listings. Zillow has rejected those claims.