The child abuse photos are a small fraction of the LAION-5B database, which contains billions of images, and the researchers argue they were probably inadvertently added as the database’s creators grabbed images from social media, adult-video sites and the open internet.

But the fact that the illegal images were included at all again highlights how little is known about the data sets at the heart of the most powerful AI tools. Critics have worried that the biased depictions and explicit content found in AI image databases could invisibly shape what they create.