1. A non-transitory computer readable recording medium storing an image processing program making a computer execute the steps of: detecting a center pixel of an isolated dot from an image; detecting an isolated dot size; extracting a tentative region based on a position of said detected center pixel of the isolated dot; and determining a dot region by correcting said extracted tentative region based on said detected isolated dot size, wherein said extracting step includes the steps of: counting the number of center pixels of isolated dots existing within a prescribed range from a process-target pixel, and comparing said counted number of the center pixels of the isolated dots with a predetermined threshold value.