Provided are an image processing device and a method for operating the same, and an endoscope processor device and a method for operating the same that accurately measure the blood vessel depth of blood vessels in an observation target. A data set including a plurality of items of measurement data in which blood vessel index values, such as blood vessel contrast and a plurality of blood vessel index value variation factors including the blood vessel depth are associated with each other is stored in a data set storage unit 97. A specific blood vessel index value variation factor other than the blood vessel depth is measured. The data set is narrowed to a sub-data set having the specific blood vessel index value variation factor. A blood vessel depth corresponding to a blood vessel index value calculated by the blood vessel index value calculation unit is found from the sub-data set.