Contactless blood pressure monitoring, includes: illuminating a blood vessel of a patient with infrared (‘IR’) light; receiving, by an IR camera through a polarizing filter, IR light reflected by the patient; capturing at a time based on a heartrate of the patient, a first IR image of the blood vessel of the patient when the blood vessel is distended; determining, from the first image, a maximum diameter of the blood vessel; capturing at a time based on the heartrate of the patient, a second IR image of the blood vessel of the patient when the blood vessel is contracted; determining, from the second IR image, a minimum diameter of the blood vessel; and calculating blood pressure of the patient in dependence upon the maximum and minimum diameters of the blood vessel.