An article on the BBC website has pointed out how each camera sensor (including phone cameras) have slight imperfections in the photo array, causing each camera to have a somewhat unique fingerprint.
“Due to imperfections in the manufacturing process of imaging sensors, the dimensions of each photosite differs ever so slightly. And when coupled with the inherent inhomogeneity of their silicon material, the ability of each photosite to convert photons to electrons varies. This results in some photosites being more or less sensitive to light than they should be, independent of what is being photographed.
So, even if you used two cameras of the same make and model to snap a uniformly lit surface – where every point on the surface has the same brightness – there’d be subtle differences unique to each camera.”
So its not just EXIF data that holds metadata in a jpeg, but the actual image capture profile. I assume you would need a few photos from the same camera to be able to pick the flaw up though.