Greek police are trying to discover the identity of a young blonde girl who was found living on a Roma settlement with a family she did not resemble.
DNA tests revealed the child, called Maria and aged about four, was not related to the couple she lived with.
The little girl is now being looked after by a charity. Her photo has been released to help find her family.
Officials believe she may have been a victim of abduction or child trafficking.
Police are appealing internationally as the girl looks like she might be from northern or eastern Europe.
The charity, Smile of the Child, told the BBC that the girl was frightened and neglected when she arrived in their care but that in overall good health and was now more relaxed.
It said it had received many calls since the appeal was launched.
A spokesman for the British couple Kate and Gerry McCann, whose daughter Madeleine went missing in Portugal in 2007, said the case gave them "great hope" that she would one day be found alive.
Police raided the Roma camp, near Farsala in central Greece, to search for drugs and weapons.
They noticed the lack of resemblance between the blonde-haired, green-eyed, pale-skinned little girl and her parents, and found further discrepancies when they investigated the family's documents.
The couple had registered different numbers of children with different regional family registries.
The woman claimed to have given birth to six children within a 10-month period.
When questioned about how they came to have Maria, the couple gave "constantly changing claims," Thessalia Province Police Director Vassilis Halatsis said.
"The girl might have been abducted from a hospital, or given up by an unmarried mother," the officer said.
"So far we do not have a declared disappearance of a child of this age in Greece. Through Interpol, we will request assistance from the other European countries."
The 39-year-old man and his 40-year-old wife have been arrested on suspicion of abducting a minor.
The president of Smile of the Child, Kostas Yannopoulos, said the girl was being used to beg on the streets.