An image processing device includes a processor including hardware, the processor being configured to: acquire an input image； detect an arc curve in the input image； determine a change in a luminance of a pixel in a direction from an inner side toward an outer side of the arc curve； detect, as a representative bubble region, a region including the arc curve involving a change determined to be an increase in the luminance in the direction from the inner side toward the outer side； and extract a bubble region, based on the representative bubble region.
