Defensive measures for residue re-imaging

1. An input device comprising:

a biometric sensor configured to capture images of a sensing region of the input device;

processing circuitry; and

a memory storing instructions that, when executed by the processing circuitry, cause the input device to:

acquire a first image of the sensing region from the biometric sensor in response to a first authentication trigger;

acquire a second image of the sensing region from the biometric sensor in response to a second authentication trigger;

determine whether an amount of similarity between the first image and the second image exceeds a threshold similarity level, the first image being different than the second image when the amount of similarity is below the threshold similarity level; and

prevent the second image from being used for user authentication responsive to determining that the amount of similarity between the first image and the second image exceeds the threshold similarity level.

2. The input device of claim 1 , wherein execution of the instructions further causes the input device to:

acquire a third image of the sensing region, wherein the third image is acquired subsequent to the first image and prior to the second image; and

determine whether an amount of similarity between the third image and the second image exceeds the threshold similarity level, wherein prevention of the second image from being used for user authentication further comprises:

determining that the amount of similarity between the third image and the second image exceeds the threshold similarity level.

3. The input device of claim 2 , wherein the third image of the sensing region is acquired periodically, or at predetermined times, or a combination thereof.

4. The input device of claim 2 , wherein the third image of the sensing region is acquired when an input object is detected in contact with or proximate to the sensing region.

5. The input device of claim 2 , wherein the third image of the sensing region is acquired based at least in part on an accelerometer, an ambient light sensor, a button press, or a combination thereof.

6. The input device of claim 1 , wherein the amount of similarity is based at least in part on a change in position between the first image and the second image, or a change in orientation between the first image and the second image, or a combination thereof.

7. The input device of claim 1 , wherein at least the second authentication trigger comprises:

a detection of an input object in contact with at least a portion of the sensing region.

8. The input device of claim 1 , wherein execution of the instructions further causes the input device to:

acquire an enrollment image during an enrollment process prior to the acquisition of the first and second images; and

authenticate the second image when the second image matches the enrollment image.

9. A method performed by one or more processors of an input device, comprising:

acquiring a first image of a sensing region from a biometric sensor in response to a first authentication trigger;

acquiring a second image of the sensing region from the biometric sensor in response to a second authentication trigger;

determining whether an amount of similarity between the first image and the second image exceeds a threshold similarity level, the first image being different than the second image when the amount of similarity is below the threshold similarity level; and

preventing the second image from being used for user authentication responsive to determining that the amount of similarity between the first image and the second image exceeds the threshold similarity level.

10. The method of claim 9 , further comprising:

acquiring a third image of the sensing region, wherein the third image is acquired subsequent to the first image and prior to the second image; and

determining whether an amount of similarity between the third image and the second image exceeds the threshold similarity level, wherein preventing the second image from being used for user authentication further comprises:

determining that the amount of similarity between the third image and the second image exceeds the threshold similarity level.

11. The method of claim 10 , wherein the third image of the sensing region is acquired periodically, or at predetermined times, or a combination thereof.

12. The method of claim 10 , wherein the third image of the sensing region is acquired when a display coupled to the input device is powered down.

13. The method of claim 12 , wherein the amount of similarity is based at least in part on a change in position between the first image and the second image, or a change in orientation between the first image and the second image, or a combination thereof.

14. The method of claim 9 , further comprising:

acquiring an enrollment image during an enrollment process prior to the acquisition of the first and second images; and

authenticating the second image when the second image matches the enrollment image.

15. A system, comprising:

a biometric sensor configured to capture images of a sensing region;

one or more processors; and

a non-transitory computer-readable medium storing instructions that, when executed by the one or more processors, cause the system to:

acquire a first image of the sensing region from the biometric sensor in response to a first authentication trigger;

acquire a second image of the sensing region from the biometric sensor in response to a second authentication trigger;

determine whether an amount of similarity between the first image and the second image exceeds a threshold similarity level, the first image being different than the second image when the amount of similarity is below the threshold level; and

prevent the second image from being used for user authentication responsive to determining that the amount of similarity between the first image and the second image exceeds the threshold similarity level.

16. The system of claim 15 , wherein execution of the instructions causes the system to:

acquire a third image of the sensing region, wherein the third image is acquired subsequent to the first image and prior to the second image; and

determine whether an amount of similarity between the third image and the second image exceeds the threshold similarity level, wherein prevention of the second image from being used for user authentication further comprises:

determining that the amount of similarity between the third image and the second image exceeds the threshold similarity level.

17. The system of claim 16 , wherein the third image of the sensing region is acquired when the system is locked, or idle for a threshold amount of time, or a combination thereof.

18. The system of claim 16 , wherein the third image of the sensing region is acquired when an input object is detected in contact with or proximate to the sensing region.

19. The system of claim 16 , further comprising:

a display coupled to the processor, wherein the third image of the sensing region is acquired when the display is powered down.

20. The system of claim 15 , wherein the amount of similarity is based at least in part on a change in position between the first image and the second image, or a change in orientation between the first image and the second image, or a combination thereof.