Apparatus for camera-based calculation of a length ratio of fingers of a hand, comprising: an image capturing unit configured to generate a still image of the hand; an image analysis unit configured to detect the fingers of the hand according to the still image by means of segmentation to obtain a binary image, wherein the binary image comprises a first partial area including the hand as well as a second partial area, wherein a first color is associated to the first partial area and a second color is associated to the second partial area; an image evaluation unit configured to determine a length of selected fingers based on the binary image and to calculate a ratio between the lengths of the selected fingers, characterized in that the image analysis unit is configured to determine a position (55a-d) of the fingers and a position (60a-d) at a circumference of the first partial area between the fingers in the binary image, wherein the image analysis unit is configured to circularly determine, starting from a fixed point in the first partial area, a distance from the fixed point to a closest point in the second partial area at differing angles, wherein local maxima in a course of the distance across the angles determine the position (55a-d) of the fingers and local minima between the maxima determine the position (60a-d) at the circumference of the first partial area between the fingers and wherein the image evaluation unit is configured to select a section of the still image or the binary image (25, 40) that is determined by a finger tip of a selected finger, first and second positions (60c, d) at a circumference of the first partial area between the fingers adjacent to the selected finger, as well as the position of the selected finger, wherein the section isolates the selected finger in the still image or in the binary image. an image capturing unit configured to generate a still image of the hand; an image analysis unit configured to detect the fingers of the hand according to the still image by means of segmentation to obtain a binary image, wherein the binary image comprises a first partial area including the hand as well as a second partial area, wherein a first color is associated to the first partial area and a second color is associated to the second partial area; an image evaluation unit configured to determine a length of selected fingers based on the binary image and to calculate a ratio between the lengths of the selected fingers, characterized in that the image analysis unit is configured to determine a position (55a-d) of the fingers and a position (60a-d) at a circumference of the first partial area between the fingers in the binary image, wherein the image analysis unit is configured to circularly determine, starting from a fixed point in the first partial area, a distance from the fixed point to a closest point in the second partial area at differing angles, wherein local maxima in a course of the distance across the angles determine the position (55a-d) of the fingers and local minima between the maxima determine the position (60a-d) at the circumference of the first partial area between the fingers and wherein the image evaluation unit is configured to select a section of the still image or the binary image (25, 40) that is determined by a finger tip of a selected finger, first and second positions (60c, d) at a circumference of the first partial area between the fingers adjacent to the selected finger, as well as the position of the selected finger, wherein the section isolates the selected finger in the still image or in the binary image.