At the top right of your screen, click "Add" and then add a "new thing." Name the page what you want. If it is a photo of some random Jones family of Memphis Tennessee, you could call the page, "Found family photo of Jones family, Memphis, Tennessee.
Once the page is created, treat it like any other profile and upload the photo to this page.
Later if you can identify the photo, location, family members, etc., you can add detail to either the photo or the page. `