Sensor-assisted biometric authentication for smartphones

1. A portable electronic device, comprising:

an imaging sensor that, selectively during operation of the portable electronic device, acquires one or more images;

a processor electrically coupled to the imaging sensor; and

memory, electrically coupled to the processor, which stores a program module that, selectively during operation of the portable electronic device, is executed by the processor, the program module including instructions for:

providing an instruction to a user to move the portable electronic device relative to a face of the user;

acquiring, using the imaging sensor, a series of images while the portable electronic device is at different positions relative to the face of the user, wherein the series of images include at least two images relative to a symmetry axis of the face of the user;

determining a change in a sign of a nose angle in at least the two images; and

authenticating the user based on at least one of the series of images using a facial-recognition technique.

2. The portable electronic device of claim 1 , wherein the portable electronic device includes a motion sensor, electrically coupled to the processor, which, selectively during operation of the portable electronic device, measures motion information; and

wherein, the program module includes instructions for associating, prior to the authenticating, the motion information with a change in a position of an object in the series of images.

3. The portable electronic device of claim 2 , wherein the motion sensor includes one of: an accelerometer, a gyroscope, a compass, an inertial motion sensor, and a magnetometer.

4. The portable electronic device of claim 2 , wherein the change in the position is based on differences in pixels in the series of images.

5. The portable electronic device of claim 2 , wherein the motion information includes vibrations and rotations of the portable electronic device.

6. The portable electronic device of claim 2 , wherein the associating involves correlating the motion information and the change in the position of the object.

7. The portable electronic device of claim 1 , wherein the series of images includes a video with multiple images.

8. The portable electronic device of claim 1 , wherein the program module includes instructions for authenticating the user while preventing successful 2D media attacks and virtual-camera attacks.

9. The portable electronic device of claim 1 , wherein the symmetry axis includes a midline of the face of the user.

10. The portable electronic device of claim 1 , wherein the instruction to move the portable electronic device specifies at least a horizontal component of the movement.

11. The portable electronic device of claim 1 , wherein the portable electronic device includes a display; and

wherein the portable electronic device includes an ambient light sensor that, during execution of the program module and when ambient light intensity in an environment of the portable electronic device is below a threshold value, increases a brightness of the display.

12. The portable electronic device of claim 1 , wherein the determining the change in the sign of the nose angle involves:

identifying regions that include a nose in the face of the user in at least the two images;

determining edges of the nose in the regions using an edge-detection technique; and

calculating the nose angle based on the determined edges.

13. A non-transitory storage medium storing instructions executable by a processor of a portable electronic device, the instructions comprising:

instructions for providing an instruction to the user to move the portable electronic device relative to a face of the user;

instructions for acquiring, using an imaging sensor in the portable electronic device, a series of images while the portable electronic device is at different positions relative to the face of the user, wherein the series of images include at least two images relative to a symmetry axis of the face of the user;

instructions for determining a change in a sign of a nose angle in at least the two images; and

instructions for authenticating the user based on at least one of the series of images using a facial-recognition technique.

14. The non-transitory storage medium of claim 13 , wherein the non-transitory storage medium includes instructions for associating, prior to authenticating, motion information from a motion sensor in the portable electronic device with a change in a position of an object in the series of images.

15. The non-transitory storage medium of claim 14 , wherein the associating involves correlating the motion information and the change in the position of the object.

16. The non-transitory storage medium of claim 13 , wherein the series of images includes a video with multiple images.

17. The non-transitory storage medium of claim 13 , wherein the instruction to move the portable electronic device specifies at least a horizontal component of the movement.

18. The non-transitory storage medium of claim 13 , further comprising instructions for increasing a brightness of a display in the portable electronic device when an ambient light sensor in the portable electronic device indicates that ambient light-intensity in an environment of the portable electronic device is below a threshold value.

19. The non-transitory storage medium of claim 13 , wherein the instructions for the determining the change in the sign of the nose angle comprise:

instructions for identifying regions that include a nose in the face of the user in at least the two images;

instructions for determining edges of the nose in the regions using an edge-detection technique; and

instructions for calculating the nose angle based on the determined edges.

20. A method for authenticating a user, wherein the method comprises:

providing an instruction to the user to move a portable electronic device relative to a face of the user;

using an imaging sensor in the portable electronic device, acquiring a series of images while the portable electronic device is at different positions relative to the face of the user, wherein the series of images include at least two images relative to a symmetry axis of the face of the user;

determining a change in a sign of a nose angle in at least the two images; and

authenticating the user based on at least one of the series of images using a facial-recognition technique.