An image processing apparatus according to an embodiment includes a processing circuitry. The processing circuitry is configured to obtain images in a time series including images of a blood vessel of a subject and correlation information indicating a correlational relationship between physical indices of the blood vessel and function indices of the blood vessel related to vascular hemodynamics, calculate blood vessel morphology indices in a time series indicating morphology of the blood vessel of the subject, on a basis of the images in the time series, and identify a function index of the blood vessel of the subject, by using a physical index of the blood vessel of the subject obtained from the blood vessel morphology indices, on a basis of the correlation information.