A computer-implemented method includes: (i) receiving location information that represents a physical location of a user; (ii) receiving a first image that has been captured by the user; (iii) in response to receiving the first image, obtaining a second image that has been captured by a camera and that depicts a particular object in an area around the physical location; (iv) determining whether the first image matches the second image; and (v) in response to determining that the first image matches the second image, determining that the user is authentic.