Document authentication by attitude-independent determination of surface appearance using controlled illumination
A user is guided to move a device equipped with an illuminator and a camera with respect to a document whose genuineness is to be assessed. The motion includes changing the distance between the device and the document by moving the device or moving the document. Imagery of the document is captured during the movement and analyzed to determine a likelihood that the document includes features indicative of genuineness, such as a hologram, an original photograph, and other regions matching those of a genuine document. The analysis may include identifying regions exhibiting large changes in appearance over relatively small distance changes which characterize holograms, and obtaining the spatial extent of document features.
1. A method of determining whether a document is genuine, the method comprising:
illuminating the document with a controlled illumination source which is in a fixed spatial relationship with a camera;
changing the distance between the camera and a centroid of the document, wherein the distance change includes a change in a distance between the camera and the centroid of the document along an axis perpendicular to a plane of she document;
using the camera to capture imagery of the document while changing the distance between the camera and the centroid of the document;
analyzing the captured imagery to obtain information about changes in appearance of a surface of the document resulting from:
changes in illumination incident on the document caused by changing a position of the controlled illumination source with respect to the document; and
changes in a position of the camera with respect to the document caused by the changing of the distance between the centroid of the document and the camera; and
analyzing the information about changes in appearance of the document to determine a likelihood that the captured imagery was captured from a genuine document.
2. The method of claim 1 , wherein the distance between the camera and the centroid of the document is changed by moving one of the camera and the document along a linear trajectory.
3. The method of claim 2 , wherein an angle between the linear trajectory and a plane of the document is less than 90 degrees.
4. The method of claim 1 , wherein the distance between the camera and the centroid of the document is changed by moving one of the camera and the document along a curved trajectory.
5. The method of claim 1 , wherein:
the camera and the controlled illumination source are components of a mobile device;
the distance between the camera and a centroid of the document is changed by a user of the mobile device; and
the user of the mobile device is instructed to move the device while keeping an image of the document displayed on a screen of the device within a specified region on the screen.
6. The method of claim 5 further comprising using the mobile device to displace the image of the document displayed on the screen of the device such that the user of the mobile device causes the mobile device to move in a desired trajectory corresponding to a trajectory in which the user of the mobile device keeps the image of the document displayed on the screen of the device within the specified region on the screen.
7. The method of claim 1 wherein the captured imagery includes imagery of a photograph within the document, and the step of analyzing the information about changes in appearance of the surface of the document includes analyzing changes in reflections from a region of the document coincident with the photograph to determine a likelihood that the captured imagery of the photograph was captured from a photograph that is not an altered photograph or a replacement photograph.
8. The method of claim 1 wherein the captured imagery includes imagery of a region adjacent to a photograph appearing within the document, and the step of analyzing the information about changes in appearance of the surface of the document includes analyzing changes in reflections from the region adjacent to the photograph to determine a likelihood that the region adjacent to the photograph was affected by at least one of alteration of the photograph and replacement of the photograph.
9. The method of claim 1 wherein the controlled source of illumination comprises a display screen.
10. The method of claim 9 , wherein the display screen displays a pattern.
11. The method of claim 9 , wherein the display screen displays a changing pattern that is controlled by at least one of a device local to the document and a remote server in data communication with a device local to the document that houses the display screen.