It is a photograph of a memorial shrine that David Thorpe created for Rosalynn Jeffries after her death. Because he was afraid his friends would think that he had gone "soft," he tried to keep its location a secret.
It can be found at the Pleasant Valley cabins, in David Thorpe's room, inside his desk and taped to the top of a drawer.
Remember our anniversary? I stole that huge stash of chems, and you found that secluded spot across from Ripper Alley. We spent that entire night under the stars. I'd never seen you happier.
Rest in peace, dear Rosalynn... wherever you may be.