1. An image processing apparatus for displaying a storyboard that lays out along one dimension a plurality of thumbnail images each of which represents a video clip, and for processing presentation-description data which designates a presentation order of a plurality of video clips including a video clip of an item of moving-image data and of a video clip of modified image data, different from the moving image data, obtained by modifying any of a plurality of items of the moving image data, comprising: a symbol image generation unit configured to generate symbol image data different from thumbnail image data representing the video clip of the modified image data, for the video clip of the modified image data; a detection unit configured to detect the video clip of the modified image data from the plurality of video clips designated by the presentation-description data according to the presentation-description data; an editing-screen generation unit configured to generate editing-screen data for an editing screen displaying the storyboard that lays out the plurality of thumbnail images of the video clips in an order according to the presentation order designated by the presentation-description data, the editing-screen generation unit laying out, if the video clip of the modified image data is detected by the detection unit, a symbol image represented by the symbol image data of the video clip of the modified image data generated by the symbol image generation unit instead of the thumbnail image of the video clip of the modified image data in the storyboard; and a display control unit configured to display the editing screen based on the editing-screen data generated by said editing-screen generation unit, on a display device.