result in reduced quality. The higher the resolution (meaning the number of pixels per inch, "ppi"), the larger the print size. Flatbed scanners typically have a hinged cover that covers the bed, and reflects light back into the scan head. This cover is usually removed or propped open when scanning 3-D objects, to prevent damage or compression of the subject. Removal of the cover also allows the artist to use additional light sources positioned above the bed, which can be used to enhance the depth captured by the scanner. Scanners can also be modified to provide additional capture abilities. For example, the scanner, with the illumination removed or disabled, can be used as a giant CCD replacement, producing a large format digital camera back at a fraction of the cost of professional large format systems. Techniques The simplest use of the scanner, which also most closely matches its use for document capture, is as a specialized tool for macro photography. As long as the subject can be placed on the scanner bed, the scanner is excellent for capturing very high resolution images, within its limitations. This also has a very practical application, as it can be used to make images of items being sold on auction sites such as eBay which are too small to be easily photographed with consumer level digital cameras. A common artistic use of the scanner is to capture collages of objects. The objects are arranged by the artist on the scanner bed, and then captured. Since the artist is working from the back of the image, it can be difficult to get the desired arrangement. Scanning software with the ability to generate a low resolution preview scan can help in obtaining the desired arrangement before the final, high resolution scan is made. Since the subjects are often placed in contact with the scanner, there is a high potential for damage to the scanner from objects scratching or cracking the surface of the bed, or from liquids that might seep from the subject into the interior of the scanner. These risks can be mitigated by placing a layer of transparent protective material, such as clear plastic film, onto the scanner bed. Another approach is to invert the scanner, so the bed is above the subject and not quite in contact with it. Capturing a moving subject with the scanner can be viewed as a problem, or