1. An image acquisition and display method, comprising: obtaining an ordinary image captured by projecting illumination light onto an observation area and receiving reflection light reflected from the observation area and a special image captured by projecting special light onto the observation area and receiving light emitted from the observation area, and displaying the obtained ordinary and special images; identifying, based on the special image, a prescribed region of interest in the special image; determining a boundary line of an area which includes a region in the ordinary image corresponding to the identified region of interest and a predetermined margin added to the region; and displaying a boundary line of the region and the boundary line of the area in the ordinary image, wherein the obtaining the ordinary image comprises capturing the ordinary image which includes a marker image of a length measurement marker including preset length information, and wherein the determining the boundary line comprises determining the predetermined margin based on a size of the marker image.