LIVENESS DETECTION
A liveness detection system comprises a controller, a video input, a feature recognition module, and a liveness detection module. The controller is configured to control an output device to provide randomized outputs to an entity over an interval of time. The video input is configured to receive a moving image of the entity captured by a camera over the interval of time. The feature recognition module is configured to process the moving image to detect at least one human feature of the entity. The liveness detection module is configured to compare with the randomized outputs a behaviour exhibited by the detected human feature over the interval of time to determine whether the behaviour is an expected reaction to the randomized outputs, thereby determining whether the entity is a living being.
1 . A liveness detection system comprising:
a controller configured to control an output device to provide randomized outputs to an entity over an interval of time;
a video input configured to receive a moving image of the entity captured by a camera over the interval of time;
a feature recognition module configured to process the moving image to detect at least one human feature of the entity; and
a liveness detection module configured to compare with the randomized outputs a behaviour exhibited by the detected human feature over the interval of time to determine whether the behaviour is an expected reaction to the randomized outputs, thereby determining whether the entity is a living being.
2 . A liveness detection system according to claim 1 , wherein the human feature that the feature recognition module is configured to detect is an eye of the entity.
3 . A liveness detection system according to claim 2 , wherein providing the randomized outputs comprises controlling the output device to emit at least one light pulse having a randomized timing within the moving image, and the expected reaction is an expected pupillary response to the at least one light pulses.
4 . A liveness detection system according to claim 3 , wherein providing the randomized outputs comprises controlling the output device to emit at least two randomly light pulse having a randomized separation in time from one another, and the expected reaction is an expected pupillary response to the at least two light pulses.
5 . A liveness detection system according to claim 3 , wherein the output device is a camera flash or a display.
6 . A liveness detection system according to claim 3 , comprising a velocity measurement module configured to compare frames of the moving image to one another so as to generate a velocity distribution of the eye, the velocity distribution representing the rate of change of the diameter of the pupil at different times, said comparison comprising comparing the velocity distribution with the expected response.
7 . A liveness detection system according to claim 6 , wherein said comparison by the liveness detection module comprises comparing the velocity distribution with a probability distribution, wherein the probability distribution represents the expected pupillary response.
8 . A liveness detection module according to claim 6 , wherein said comparison by the liveness detection module comprises:
determining a first time, wherein the first time corresponds to a local maximum of the velocity distribution;
determining a second time, wherein the second time corresponds to a local minimum of the velocity distribution, the local minimum occurring immediately before or immediately after the local maximum; and
determining a difference between the first and second times and comparing the difference to a threshold.
9 . A liveness detection module according to claim 8 , wherein respective differences are determined between the first time and two second times, one corresponding to the local minimum immediately before the local maximum and one corresponding to the local minimum occurring immediately after the local maximum, and each is compared to a respective threshold.
10 . A liveness detection system according to claims 7 and 9 , wherein the entity is determined to be a living being only if each of the two differences is below its respective threshold, and the velocity distribution matches the probability distribution.
11 . A liveness detection system according to claim 1 , wherein the output device is a display.
12 . A liveness detection system according to claims 2 and 11 , wherein providing the randomized outputs comprises controlling the display to display a display element at a random location of the display, and the expected reaction is an expected movement of the eye.
13 . A liveness detection system according to claim 12 , comprising:
a spatial windowing module configured to identify, for each of a plurality of frames of the moving image, an iris area, the iris area corresponding to the iris of the eye in the frame;
an analysis module configured to, for each of a plurality of regions of the iris area, generate a histogram of pixel values within that region for use in tracking movements of the eye, the liveness detection module being configured to perform said comparison by comparing the histograms with the expected movement.
14 . A liveness detection system according to claim 13 , wherein the liveness detection module is configured to perform said comparison by comparing the histograms with a probability density function representing the expected movement.
15 . A liveness detection system according to claim 12 , comprising:
a spatial windowing module configured, for each of a plurality of frames of the moving image, to divide at least a portion of that frame into a plurality of blocks, each block formed one or more respective sub-blocks, each sub-block formed of one or more respective pixels; and
an analysis module configured to assign to each block a respective block value based on its one or more respective sub-blocks, the liveness detection module being configured to perform said comparison by comparing the block values with the expected movement.
16 . A liveness detection system according to claim 15 , wherein each sub-block is formed of a multiple pixels, and/or each block is formed of multiple sub-blocks.
17 . A liveness detection system according to claim 15 , wherein the analysis module is configured to assign to each sub-block a binary value by detecting whether or not at least a predetermined proportion of its respective pixels have intensities below an intensity threshold, the block value of each block being assigned by combining the binary values assigned to its respective sub-blocks.
18 . A liveness detection system according to claim 17 , wherein the pixel intensities are determined by converting the plurality of frames from a colour format into a grayscale format.
19 . A liveness detection system according to claim 12 , wherein providing the randomized outputs further comprises accessing user-created data, held a first memory local to the output device, which defines a restricted subset of locations on the display, the random location being selected at random from the restricted subset, wherein the system is also configured to compare the behaviour exhibited by the eye with a version of the user-created data held in a second memory remote from the output device.
20 . A liveness detection system according to claim 19 , wherein the first memory and the output device are integrated in a user device.
21 . A liveness detection system according to claim 19 , wherein the user-created data defines a two-dimensional curve, the restricted subset being the set of points on the curve.
22 . A liveness detection system according to claim 2 , wherein the behaviour that is compared with the randomized outputs is at least one of:
changes in the size of the pupil of the eye over time;
changes in an iris pattern of the eye over time; and
eye movements exhibited the eye.
23 . A liveness detection system according to claim 1 , wherein providing the randomized outputs comprises controlling the output device to output at least one randomly selected word;
wherein the human feature that the feature recognition module is configured to detect is a mouth of the entity, and the expected response is the user speaking the word, the movements of the mouth being compared to the random word using a lip reading algorithm.
24 . A liveness detection system according to claim 1 , comprising an access module configured to grant the entity access to a remote computer system only if they are determined to be a living being.
25 . A liveness detection system according to claim 1 wherein the liveness detection module is configured to output at least one of: a confidence value which conveys a probability that the entity is a living being, and a binary classification of the entity as either living or non-living.
26 . A computer-implemented liveness detection method comprising:
controlling an output device to provide randomized outputs to an entity over an interval of time;
receiving a moving image of the entity captured by a camera over the interval of time;
processing the moving image to detect at least one human feature of the entity; and
comparing with the randomized outputs a behaviour exhibited by the detected human feature over the interval of time to determine whether the behaviour is an expected reaction to the randomized outputs, thereby determining whether the entity is a living being.
27 . A computer program product comprising computer readable instructions stored on a non-transitory computer readable storage medium and which, when executed, configured to implement a method comprising:
controlling an output device to provide randomized outputs to an entity over an interval of time;
receiving a moving image of the entity captured by a camera over the interval of time;
processing the moving image to detect at least one human feature of the entity; and
comparing with the randomized outputs a behaviour exhibited by the detected human feature over the interval of time to determine whether the behaviour is an expected reaction to the randomized outputs, thereby determining whether the entity is a living being.