The Gravatar integration module integrates Drupal user pictures with the service provided by Gravatar in such a way that allows the user not to upload a picture, but use the default that's associated with her email, and lets Drupal use that picture as her user picture.
Steps to reproduce: Install gravatar.module & ds.module, set up a user with a Gravatar-provided picture (it does get displayed on the user's profile page), set up a DS layout to use the user's picture: it doesn't get displayed.
Error: When Display Suite renders a user's picture, and that user does not have an "own", uploaded picture, but only a Gravatar-provided one, it does not get displayed. (If the user has her "own", uploaded picture, it does get displayed, though.)
Expected behavior: DS should display the Gravatar-provided user picture( replacement)s as well.