1. A method for distinguishing living cells during cell observation, comprising: obtaining a first image and a second image of an object positioned in an observation field of view by an imaging device, the first image and the second image being taken at a predetermined time interval; extracting a first representation of the object shown in the first image and a second representation of the object shown in the second image, and aligning the rotational angular orientation of the object in the image plane; computing a correlation value or a difference between the first representation and the second representation in which the rotational angular orientation has been aligned; and determining whether the object is a living cell based on the computed correlation value or difference.