After studying hours of videotape from the hospital's security cameras, officers have located a blurred image of a woman which is now being enhanced by computer experts.
Nottinghamshire police would give no details of the image or when it would be released. But a spokesman said they were 'hopeful' it would prove helpful in the increasingly desperate search to find Abbie.
A week ago, police released two video shots of a back view of the woman taken by a security camera and three photofit pictures based on descriptions given by Abbie's father Roger, a hospital worker and two other witnesses. But the thousands of calls which followed failed to lead to Abbie.
Officers believe Abbie's abductor entered the Queen's Medical Centre, disguised in a black wig and a nurse's uniform and changed into leggings to make her escape after persuading Mr Humphries, 33, to hand his four- hour-old daughter over for a 'routine hearing check'.
'The image is at the laboratory,' a police spokesman said. 'Before it is released, we have to believe it will be helpful to the investigation. But we are hopeful it will be more helpful than the photofits which were all different and could have been misleading.'
Detectives are still relying heavily on public vigilance to lead them to Abbie and end the torment of her parents.
Detective Superintendent Harry Shepherd, leading the inquiry, and Paul Britton, a psychologist advising the police, are working on the theory that the kidnapper is a woman who has lost or cannot have a child of her own. But repeated pleas from the police and Abbie's family for the kidnapper to get in touch, even to say the baby is safe and well, have failed. A second appeal from Josie Clark, sister of Abbie's mother, Karen, to the abductor on Wednesday has brought no new leads.
Inspector David Gilbert, spokesman for the investigation team, warned yesterday that Abbie's kidnapper might be fooling neighbours by pretending that the child is a boy.
He urged the public to have no preconceived ideas about judging suspicious circumstances. He also warned that although Abbie was blonde when she was born, the colour could now have altered.
'There may be people who have noticed someone has not been turning up for work,' he added. 'That is a consideration - why hasn't that person been turning up for work? Ask yourselves that.'
He also asked milkmen and postmen to be alert for something unusual and asked holidaymakers to report anything suspicious. The baby could have been taken straight to a caravan, a holiday flat or a hotel, he said.
Meanwhile, David Bailey, the photographer, has criticised police after his wife Catherine, 32, was arrested on Wednesday in a London department store with her three-week-old son Sasha.
Scotland Yard said she was arrested because she refused to give personal details but Mr Bailey said this was not true. Mrs Bailey, who bears some resemblance to the photofits, has been stopped twice by police seeking Abbie.