Q: Preview won't capture signature

When I go to add a signature in Preview, I hold the signature up to the camera and nothing happens. I've seen videos of people doing the same thing and Preview instantaneously shows a preview of their signature. I do not have the same luck. Pressing Accept just closes the window and doesn't add a signature. I'm unsure what to do now, as I need to add a signature to a PDF document and would rather not take a picture of the screenshot and paste it into the original Word document.