But some experts were skeptical, dismissing the claim as another spin-off of Dan Brown's best-selling novel "The Da Vinci Code."
Slavisa Pesci claims to have discovered new images in the 15th mural in the dining hall of Milan's Santa Maria delle Grazie church by superimposing a reverse image on the original image.
When doing so, Pesci said he observed, for example, that the two figures on either end of the long table appear to become knights, and that another figure appears to be holding an infant.
"It came to mind to scan 'The Last Supper' and print it on transparent paper, then superimpose it in reverse on the original image. The result is a new painting, with other figures," Pesci said Wednesday at a news conference.
Pesci assigned no meaning to the images, saying he was not an art historian, but suggested it might have reflected Leonardo's well-known interest in mathematics.
But Alessandro Vezzosi, a Leonardo expert and the director of a museum dedicated to the artist in his hometown of Vinci, was skeptical, saying "The Last Supper" was so degraded by time that it was difficult to draw any new conclusions.
While he had not yet seen the presentation, he noted that computers lend themselves to any conceivable alterations and that some have inaccurately held that the artist's famed "Mona Lisa" is actually a self-portrait.
"I don't like to be negative, because I admire discoveries reached scientifically," Vezzosi said. "If this computer analyst did not make a historic discovery, I hope he created something artistically beautiful."
Reinterpretations of the painting have popped up ever since "The Da Vinci Code" fascinated readers and movie-goers with suggestions that one of the apostles sitting on Jesus' right is Mary Magdalene, that the two had a child and that their bloodline continues.