1. A method for manufacturing a single crystal comprising: photographing an image of a boundary portion between the single crystal and a melt by a camera during a single crystal pull-up process according to a Czochralski method; comparing at least one pixel included in a left side region with respect to an extension line of a pull-up shaft of the single crystal and at least one pixel included in a right side region with respect to the extension line; and determining an abnormality in a luminance distribution of the image from a result of the comparing, wherein the luminance distribution of the image is determined to be abnormal when a luminance difference between a first maximum luminance in the left side region and a second maximum luminance in the right side region is equal to or larger than a threshold.