Spoof detection via 3D reconstruction

1. A method comprising:

receiving, at one or more processing devices, a first sequence of images of a first subject captured by an image acquisition device over a time period in which relative locations of the image acquisition device with respect to the first subject varies;

selecting, by the one or more processing devices, a first image and a second image from the first sequence of images, wherein the first image represents a first relative location of the image acquisition device with respect to the first subject, and the second image represents a second relative location, different from the first relative location, of the image acquisition device with respect to the first subject;

generating, by the one or more processing devices and using the first image and the second image as a stereo pair, a first three-dimensional representation of the first subject using a photometric stereo process for estimating a three dimensional shape from two dimensional images;

determining, based on the first three dimensional representation, that the first subject is an alternative representation of a live person; and

responsive to determining that the first subject is an alternative representation of a live person, preventing access to a secure system.

2. The method of claim 1 , wherein the image acquisition device is a camera disposed on a mobile device, and the sequence of images are captured as the mobile device is moved towards the first subject.

3. The method of claim 1 , wherein the image acquisition device is a camera disposed on a kiosk device, and the sequence of images are captured as the first subject moves towards the kiosk device.

4. The method of claim 1 , wherein the alternative representation of the live person comprises a photograph of the live person printed on paper, or presented on a display device.

5. The method of claim 1 , wherein the photometric stereo process comprises a structure-from-motion process.

6. The method of claim 1 , wherein the photometric stereo process comprises a shape-from-shading process.

7. The method of claim 1 , further comprising:

receiving, at the one or more processing devices, a second sequence of images of a second subject captured by the image acquisition device over a time period in which relative locations of the image acquisition device with respect to the second subject varies;

selecting, by the one or more processing devices, a third image and a fourth image from the second sequence of images, wherein the third image represents a first relative location of the image acquisition device with respect to the second subject, and the fourth image represents a second relative location, different from the first relative location, of the image acquisition device with respect to the second subject;

generating, by the one or more processing devices and using the third image and the fourth image as a stereo pair, a second three-dimensional representation of the second subject;

determining, based on the second three dimensional representation, that the second subject is a live person; and

responsive to determining that the second subject is a live person, initiating an authentication process for the live person to access the secure system.

8. An system comprising:

an image acquisition device configured to capture a first sequence of images of a first subject over a time period in which relative locations of the image acquisition device with respect to the first subject varies; and

an image analysis engine comprising one or more processing devices, wherein the image analysis engine is configured to:

receive the first sequence of images,

select a first image and a second image from the first sequence of images, wherein the first image represents a first relative location of the image acquisition device with respect to the first subject, and the second image represents a second relative location, different from the first relative location, of the image acquisition device with respect to the first subject,

generate, using the first image and the second image as a stereo pair, a first three-dimensional representation of the first subject using a photometric stereo process for estimating a three dimensional shape from two dimensional images,

determine, based on the first three dimensional representation, that the first subject is an alternative representation of a live person, and

responsive to determining that the first subject is an alternative representation of a live person, prevent access to a secure system.

9. The system of claim 8 , wherein the image acquisition device comprises a camera disposed on a mobile device, and the sequence of images are captured as the mobile device is moved towards the first subject.

10. The system of claim 8 , wherein the image acquisition device is a camera disposed on a kiosk device, and the sequence of images are captured as the first subject moves towards the kiosk device.

11. The system of claim 8 , wherein the alternative representation of the live person comprises a photograph of the live person printed on paper, or presented on a display device.

12. The system of claim 8 , wherein the photometric stereo process comprises a structure-from-motion process.

13. The system of claim 8 , wherein the photometric stereo process comprises a shape-from-shading process.

14. The system of claim 8 , wherein the image analysis engine is configured to:

receive a second sequence of images of a second subject captured by the image acquisition device over a time period in which relative locations of the image acquisition device with respect to the second subject varies;

select a third image and a fourth image from the second sequence of images, wherein the third image represents a first relative location of the image acquisition device with respect to the second subject, and the fourth image represents a second relative location, different from the first relative location, of the image acquisition device with respect to the second subject;

generate, using the third image and the fourth image as a stereo pair, a second three-dimensional representation of the second subject;

determine, based on the second three dimensional representation, that the second subject is a live person; and

responsive to determining that the second subject is a live person, initiate an authentication process for the live person to access the secure system.

15. One or more non-transitory machine-readable storage devices having encoded thereon computer readable instructions for causing one or more processing devices to perform operations comprising:

obtaining a first sequence of images of a first subject captured by an image acquisition device over a time period in which relative locations of the image acquisition device with respect to the first subject varies;

selecting a first image and a second image from the first sequence of images, wherein the first image represents a first relative location of the image acquisition device with respect to the first subject, and the second image represents a second relative location, different from the first relative location, of the image acquisition device with respect to the first subject;

generating, using the first image and the second image as a stereo pair, a first three-dimensional representation of the first subject using a photometric stereo process for estimating a three dimensional shape from two dimensional images;

determining, based on the first three dimensional representation, that the first subject is an alternative representation of a live person; and

responsive to determining that the first subject is an alternative representation of a live person, preventing access to a secure system.

16. The one or more non-transitory machine-readable storage devices of claim 15 , wherein the image acquisition device is a camera disposed on a mobile device, and the sequence of images are captured as the mobile device is moved towards the first subject.

17. The one or more non-transitory machine-readable storage devices of claim 15 , wherein the image acquisition device is a camera disposed on a kiosk device, and the sequence of images are captured as the first subject moves towards the kiosk device.

18. The one or more non-transitory machine-readable storage devices of claim 15 , wherein the operations further comprise:

obtaining a second sequence of images of a second subject captured by the image acquisition device over a time period in which relative locations of the image acquisition device with respect to the second subject varies;

selecting a third image and a fourth image from the second sequence of images, wherein the third image represents a first relative location of the image acquisition device with respect to the second subject, and the fourth image represents a second relative location, different from the first relative location, of the image acquisition device with respect to the second subject;

generating using the third image and the fourth image as a stereo pair, a second three-dimensional representation of the second subject;

determining, based on the second three dimensional representation, that the second subject is a live person; and

responsive to determining that the second subject is a live person, initiating an authentication process for the live person to access the secure system.

19. The one or more non-transitory machine-readable storage devices of claim 15 , wherein the alternative representation of the live person comprises a photograph of the live person printed on paper, or presented on a display device.

20. The one or more non-transitory machine-readable storage devices of claim 15 , wherein the photometric stereo process comprises a structure-from-motion process or a shape-from-shading process.