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 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 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 . <EOS>