It is an object of the present invention to provide an image processing apparatus, an endoscope system, an image processing method, and an image processing program capable of accurately estimating blood vessel information, and a recording medium on which such an image processing program is recorded. An image processing apparatus according to an aspect of the present invention includes: an image acquisition unit that acquires an image of a living body； a blood vessel index value calculation unit that calculates a blood vessel index value of the living body from the acquired image； a blood vessel density calculation unit that calculates a blood vessel density of the living body from the acquired image； a blood vessel index value correction unit that corrects the calculated blood vessel index value according to the calculated blood vessel density； and a blood vessel information estimation unit that estimates blood vessel information of the living body based on the corrected blood vessel index value. In such an image processing apparatus, the blood vessel index value is corrected according to the blood vessel density in consideration of the influence of interference according to the blood vessel density, and the blood vessel information of the living body is estimated based on the corrected blood vessel index value. Therefore, blood vessel information can be accurately estimated.
