A snatched picture purporting to be of Madeleine McCann in north Morocco was published last night, generating new momentum in the search for her.

Gerry and Kate McCann called last night for the picture, taken on August 31 by a Spanish tourist and handed to the McCanns’ lawyers yesterday morning, to be fully investigated.

The picture shows a light-skinned, blonde-haired girl being carried in a sling on a Moroccan woman’s back near the town of Zinat. It is the fourth reported sighting of a girl fitting Madeleine’s description in Morocco since she disappeared on May 3 but the first published picture.

A Spanish newspaper reported yesterday that another tourist saw a girl resembling Madeleine as she drove through the town of Zaio in northern Morocco at the end of May.

The woman said that Portuguese police were not interested in her report because they assumed that Madeleine was already dead.

Clarence Mitchell, a spokesman for the McCanns, said last night: “The picture poses serious questions. The child does appear to look like Madeleine. Kate and Gerry are keen to establish what exactly we are seeing here.”

Clara Torres, a tourist from Albacete, Spain, who took the picture published last night, said that she had thought immediately of the missing toddler. She told the Spanish radio station COPE last night: “As soon as I took the photo we were struck by the little girl, who was very blonde. Then yesterday [Monday] we heard on the news that there were various people who said they had seen Madeleine in Morocco. I ran to the computer, down-loaded the photos and started to amplify the photo, and when we saw it we realised yes, it could be her. It sent shivers down my spine.

“Although it’s not 100 per cent certain, there’s a strong possibility it could be Madeleine and if it is it could provide a twist to everything that has happened.”

She said she handed the photograph, for which she has not received any payment, into the British Embassy and spoke to the McCanns’ lawyers yesterday morning after deciding that Spanish authorities were taking too long to carry out tests on the picture.

Mr Mitchell said yesterday: “This picture was brought to the attention of the relevant authorities as soon as we received it. Kate and Gerry are naturally very keen for it it to be thoroughly investigated as quickly as possible.”

It is expected that it will now be analysed by the Child Exploitation and Online Protection centre using face-mapping technology.

The latest development comes after a report from another Spanish woman who is convinced that she saw Madeleine in the town of Zaio in northern Morocco at the end of May.

The woman said that she saw a girl she believed was Madeleine being led by a Moroccan woman in Muslim dress. It is reported that a gust of wind blew the child’s hat off, revealing her blonde hair underneath.

There were two sightings of a blonde girl matching Madeleine’s description in Marrakesh on May 9. The tourists who reported the sightings have both complained of a lack of interest from detectives.

Mr and Mrs McCann have also been concerned at the apparent lack of efforts by police to follow up potential sightings of Madeleine, particularly in Morocco.

Mrs McCann has always believed that her daughter could have been smuggled to Morocco within hours of her disappearance. The 30-minute ferry crossing from Spain to Tangiers is a five-hour drive from Praia da Luz, where the family were holidaying when Madeleine disappeared.

Later a source close to the family said: “The McCanns are not going to get their hopes up until the photograph has been sent for forensic examination. It obviously needs a lot of work done on it.”

A spokesman for the Spanish Government said last night: “The police are taking the claim seriously enough to have sent it on to their colleagues at Interpol.”

The picture was published as it emerged that the McCanns could be prosecuted for using a private security company in the search for their daughter, even though a senior Portuguese prosecutor admitted that she may have been abducted. The use of investigators by the McCanns has led to deep concern among the police and judicial authorities in Portugal, where it is illegal for private detectives to become involved in criminal cases.

A source close to the McCanns’ legal team has confirmed the involvement of Control Risks Group (CRG), but insisted that it is simply providing advice on the search for Madeleine. He said: “You can assume that they are doing some things that the Portuguese police can’t do.” Private investigators unconnected to CRG are believed to be already working in Morocco, Portugal and Spain.