An image processing device which includes a computer processor, the image processing device comprising: an acquisition unit configured to acquire an image which includes a first region and a second region of a user, the first region consisting of a dorsum of a hand and a portion from a second joint to a third joint of a finger of the hand, and the second region consisting of a region from the fingertip to the second joint of the finger of the hand; an extraction unit configured to extract the plurality of candidate areas based on a predetermined first pixel value, the predetermined first pixel value being determined in advance based on differences between pixel values of adjacent pixels in regions including wrinkles of skin existing on the first joint and second joint of a finger and differences between pixel values of adjacent pixels in boundary portions between first region and second region and background area; a detection unit configured to detect, from a plurality of candidate areas for the first region and the second region included in the image, a first candidate area corresponding to the first region based on a predetermined image feature of the first region, wherein the predetermined image feature includes at least one of an area of the first region, a shape of the first region, mean of the pixel values of the first region, and variance of the pixel values of the first region, determined in advance by measuring a typical first region; a determination unit configured to determine parallel lines included in outer edges of the first candidate area; and a selection unit configured to select a second candidate area corresponding to the second region from the plurality of candidate areas based on the parallel lines. an acquisition unit configured to acquire an image which includes a first region and a second region of a user, the first region consisting of a dorsum of a hand and a portion from a second joint to a third joint of a finger of the hand, and the second region consisting of a region from the fingertip to the second joint of the finger of the hand; an extraction unit configured to extract the plurality of candidate areas based on a predetermined first pixel value, the predetermined first pixel value being determined in advance based on differences between pixel values of adjacent pixels in regions including wrinkles of skin existing on the first joint and second joint of a finger and differences between pixel values of adjacent pixels in boundary portions between first region and second region and background area; a detection unit configured to detect, from a plurality of candidate areas for the first region and the second region included in the image, a first candidate area corresponding to the first region based on a predetermined image feature of the first region, wherein the predetermined image feature includes at least one of an area of the first region, a shape of the first region, mean of the pixel values of the first region, and variance of the pixel values of the first region, determined in advance by measuring a typical first region; a determination unit configured to determine parallel lines included in outer edges of the first candidate area; and a selection unit configured to select a second candidate area corresponding to the second region from the plurality of candidate areas based on the parallel lines.