A mother has recognised her own four-year-old daughter after German police released a still image of a child in an attempt to find her abuser.
The picture was taken from videos and images circulating on the dark web.
A 24-year-old man has now been arrested.
The police said that they took the unusual step of releasing the image because they had been unable to identify the attacker.
They received "numerous" responses from the public, following the release of the image.
The man - from Wesermarsch - faces charges of the serious sexual abuse of children plus the production and distribution of images of child abuse.
The case involved teams from the Federal Criminal Police Office, the Central Office for Combating Internet Crime and Frankfurt's prosecutors' office.
They thanked the public for their help.
The videos and images were discovered in July but it is believed that the abuse had been going on since October last year.
The abuser was known to the child, according to the police.
Jim Gamble, former chief executive of the UK's Child Exploitation and Online Protection unit, said releasing such images should be the "last resort" for law enforcement.
"Other options would include public circulation of pictures of furniture associated with the location of the abuse and/or particular clothes worn by the child. An actual identifiable facial image is and should always be the last resort," he told the BBC.
"At the end of the day this is a real child, subject to ongoing abuse so if all the other areas have been exhausted, wider circulation is the right thing in my opinion."
But, he added, it was important to make criminals aware that the dark net is not a place to "hide" such images and videos.
"The dark net is not a no-go area to law enforcement and neither should it be," he said.
"At the end of the day we cannot allow the technology to dictate tactics or to prevent us from focusing on the real issue: people who threaten our children."