An image forming apparatus (100) extracts from first image data (11) second image data (12), which is image data of a document, and accepts operation for selecting either a first preview image (71) corresponding to the first image data (11) or a second preview image (72) corresponding to the second image data (12). The image forming apparatus (100) outputs, when the first preview image (71) is selected, the first image data (11) and, when the second preview image (72) is selected, the second image data (12).