There is provided an apparatus for processing an on-screen display (OSD), the apparatus including: a buffer unit receiving first dynamic guideline image information, a color determining unit determining colors for previously divided sections included in the first dynamic guideline image information from the buffering unit, and an image synthesizing unit synthesizing second dynamic guideline image information having the colors for each of the sections, determined by the color determining unit with an image from a camera. With the apparatus for processing an OSD, a user freely sets colors of a warning message, a static guideline, and a dynamic guideline, whereby the warning message, the static guideline, and the dynamic guideline can be displayed on a screen without obscuring a rearview image. In addition, a dynamic guideline can be set as different colors according to sections divided into distances from the rear of a vehicle and an image can be continuously displayed. Further, the camera module can be reprogrammed.