The photograph, published on many newspaper Web sites, shows a woman walking along a road and carrying a fair-haired child on her back. It was reportedly taken last month by Spanish tourists in northern Morocco.
"We understand that the photo has been sent to the relevant authorities and is being analyzed," said Adrian Chapman, a British Embassy spokesman in Rabat, the Moroccan capital.
A spokesman for the Moroccan Interior Ministry could not be immediately reached for comment and Portuguese police declined to comment on the grounds that an investigation was continuing.
The couple said they had left the girl and her younger twin siblings asleep in their rented villa while they had dinner nearby. Despite an extensive search and a worldwide publicity effort led by her parents, no confirmed trace of the child has turned up.
Alleged sightings of the girl have already been reported in Europe and Morocco. The area in which the photograph was taken is known for European influences, and fair-haired children with light-colored eyes are relatively common in the North African kingdom.
"On the face of it, it looks significant," said Clarence Mitchell, a spokesman for the couple, of the photo. He said the McCanns were being kept informed, and were awaiting the results of the police investigation.
Mitchell said he and the family "took a decision a long time ago not to comment on these sightings, because they have all proved false."
Interpol did not immediately respond to calls and an e-mail from The Associated Press seeking comment. News reports said the international police body, based in Lyon, France, had received the photo from Portuguese police.