A police source told the New York Post the snapshot was found on Bashid McLean's cell phone. There were other photographs of the corpse as well.
"I lost sleep over it -- just sheer inhumanity," the source said Friday. "It's horrible what he did to her."
McLean, 23, was arrested after the body of his mother, Tanya Byrd, 45, was found in trash bags dumped in different locations in the Morrisania neighborhood in the Bronx.
William Harris, 26, has been charged with helping McLean dispose of his mother's corpse.
At his arraignment, McLean, dressed only in a garbage bag, denied the killing. He and Harris are scheduled to appear in court again Monday.
Investigators say McLean was angry because she wanted him to move out of the Morrisania apartment she shared with him and his younger brother, who has Down's syndrome.
Cassandra McLean-Smith, McLean's aunt, said the familiy is "horrified" by the crime.
"We don't know this person," McLean-Smith said. "We don't know where he comes from -- if it is the same blood that runs through our veins runs through his veins. He is a monster. We are sorry that New York doesn't have the death penalty. We want death."