Doctors should be cautious when examining "amateur" photographs of marks on children, a family court judge has warned.
Judge Joanna Vincent said pictures taken on mobile phones can be unreliable.
She raised concern after overseeing a case in which social workers intervened when doctors thought mobile phone photographs showed bruises on a two-month-old baby.
The judge said no clinician who had examined the girl in person had identified a bruise and the only "means of diagnosis" was the photographs.
She said she could not have concluded that the marks were bruises having examined all available evidence.
Judge Vincent said there were "lessons to be learned" from the case.
The judge, who examined evidence at a family court hearing in Oxford earlier this month and has outlined concern in a written ruling, said the baby could not be identified.
"It is important to be aware that photographic imagery taken at amateur level may misrepresent what is present in fact," said the judge.
"Other factors which affect the reliability of photographic imagery include the light exposure and device used.
"When examining photographic images of suspicious marks, knowledge of the date and time and circumstances in which the photographs were taken would assist and ought as far as possible to be compared to any contemporaneous account of matters (marks) seen, whether by a medical professional or carer."
Judge Vincent said the girl's mother had taken pictures showing marks on the baby's face.
Council social services bosses had asked the judge to consider taking the girl from her parents' care after a GP and consultant paediatrician thought the photographed marks were bruises.
But bosses had changed their minds after reviewing evidence.