An inquiry team set up in London by opposition groups said some pictures were smuggled out of the country by a defector. They said some depict victims with signs of torture and marks of beatings, while others show extreme emaciation suggestive of starvation.
The international team, which includes Scottish forensic anthropologist Susan Black, Professor of Anatomy and Forensic Anthropology at the University of Dundee, said the cache provided strong evidence for charging president Bashar Assad and others for crimes against humanity. The report - commissioned by the Qatar government, one of the countries most deeply involved in the Syrian conflict and a major backer of the opposition - could not be independently confirmed.
Special prosecutor David Crane, a lawyer and member of the team, said: "What happens next will be a political and diplomatic decision. It's chilling; it's direct evidence to show systematic killing of civilians."
More than 130,000 people have died in Syria's conflict, and more than a quarter of the population of 23 million now live as refugees, either within Syria or in neighbouring countries.
Fighters who took up weapons against Mr Assad have turned their guns on each other, trapping Syrians in the violence of two wars.