That looks like the mounting plate for your fan off to the side of your photo. See if the mounting holes will adjust outward past the sides of the box. This box is likely screwed into your ceiling framing with those four silver screw heads that run in a line through the middle of it. Following that line past the sides of your box, use 3" construction screws to run through the mounting plate and between the outside edge of the box and your drywall. They should find the ceiling framing. Mounting like that would be secure enough to hang any ceiling fan from.