1. An image processing device comprising: a detector that detects a target pixel as an outline pixel if a density of a predetermined region including the target pixel with each pixel of an image treated as the target pixel is equal to or above an outline determination threshold value, the outline determination threshold value being a threshold value set in response to the density of the target pixel, and being a threshold value used to determine whether the target pixel is an outline pixel corresponding to an outline of the image; and a correction unit that corrects a correction pixel, as a correction target having a density equal to or above a predetermined density from among the outline pixels detected by the detector, in response to a density of the correction pixel.