Most scanners today are variations on the desktop (or flatbed) scanner, which analyzes a physical 2D image (such as a photograph, text document, or handwriting) or an object (such as a relief sculpture) and converts it to a digital image. The features to consider when purchasing a scanner are: optical resolution, color depth, the availability of a transparency adapter, the availability of an automatic document feeder (ADF), and the connectivity interface. As with digital cameras, the higher the resolution and color depth of the scanner, the better the output quality.
Transparency adapters and ADFs are additional features that one may or may not need. Transparency adapters allow for scanning slides or film negatives and come with film trays that hold the various media. ADFs are helpful when handling high volumes of optical character recognition scans. However, since it is usually more expensive to buy a scanner separately from an ADF, if you are considering this feature, you will want to find a scanner that includes an ADF at the outset.
The amount of data generated by a scanner can be very large and requires a fast connection with the computer. Some of the interfaces available are parallel, USB, USB2, and Firewire connections. Parallel interfaces transmit data at 70 kilobytes (KB) per second (ps), USB at 1MBps, USB2 at 40MBps, and Firewire at 400MBps. Depending on its features, flatbed scanners can cost from $50 to $700.