A method for estimating a blur kernel distribution for the visual iris recognition includes determining a first mathematical relationship between a focus position of a camera lens and a distance between the lens and an iris, whose image is to be captured by the camera. The first relationship is used to estimate a second mathematical relationship between the focus position of the lens and a standard deviation, defining a Gaussian blur kernel distribution. A position of an eye of a living being at a future time is predicted. A focus position of the camera lens is adjusted on the basis of the predicted position of the eye. The camera lens with the focus adjusted position is used to produce an image of the eye of the subject at the time. An actual position of the eye of the subject at that time is detected. The first relationship is used to determine a desired position of the focus lens on the basis of the actual position of the eye of the subject at the time. The second relationship is used to calculate a standard deviation, defining a Gaussian blur kernel distribution. The calculation is based on a difference between the set focus position and desired focus position of the lens.