An object of the present invention is to provide an image processing apparatus and a computer program which detects a defect such as a scum at high speed and with high precision. In order to accomplish the above-described object, the present invention proposes an image processing apparatus and a computer program which acquires image data, and detects edge branch points from this image data. Here, at each of the edge branch points, an edge associated therewith branches off in at least three or more directions. According to this configuration, it becomes possible to detect a defect such as a scum without utilizing the reference-pattern image. As a consequence, it becomes possible to detect the scum at high speed and with high precision.