What do you need to scan? What type of scanner you need largely depends on what, as well as how often, you'll need to scan. Flatbed scanners are the most practical for multipurpose use. They're generally more versatile and cheaper than scanners geared toward a specific function. They're a safe bet if you'll be scanning delicate material such as photos, film or slides, and they're essential for handling 3D objects or bound material like books and magazines. Those who need to create digital copies of lots of loose pages and documents should consider a sheet-fed scanner, which are designed specifically for this task. High-end photo scanners are relatively expensive, but they're the best for high-resolution scans of images. They're also ideal for scanning film, slides, or negatives, although some basic flatbed scanners can handle these materials also. If you need to scan unusually shaped items, such as business cards or three-dimensional objects, look for a scanner specifically designed to handle these tasks.
What resolution do you need? If you're scanning plain-text documents or documents with business graphics, resolution isn't a huge concern – experts say 200 dpi is adequate, and 300 dpi is plenty. New scanners typically have resolutions of least 600 dpi, which is sufficient for images, as long you don't enlarge them too much or zoom in too far. For the finest detail or printing scans at a larger size, you'll need a scanner with a higher resolution – at least 4,800 dpi. Editors at PCMag.com note that you should take claimed resolutions with a grain of salt, as these specs are often inflated or are bottlenecked by the scanner's optical hardware. However, as a rule of thumb, the higher a scanner's claimed resolution, the higher its real-world resolution is likely to be.
What about color depth? Color depth is a measurement of how many variations of colors the scanner can see. It's generally not important on document scanners, but it is very important for scanning photos and drawings. Photo scanners typically have 48-bit color depth.
Do you scan in bulk? If you plan to churn through huge stacks of paper on a regular basis, an automatic document feeder (ADF) is a must. Look for an ADF with a capacity greater than or equal to the number of pages you typically need to scan at a go. If you have to scan a longer document once in a while, you can always add more pages partway through the process.
How big are your documents? The larger the scanning area, the larger the document or photo you can reproduce (and the larger number of smaller images you can scan at a time). Most flatbed scanners can only accommodate letter-size documents, so if you need to scan legal-size pages or large pieces of artwork, look for a larger scanbed.
Do you need duplex scanning? There are several ways to scan two-sided documents. True duplexing scanners have two scanning elements, so they can scan both sides of a page at once. Other scanners have an ADF with duplexing capabilities; it scans one side of the page, flips it, and scans the other. Duplexing scanners are faster, but they're also more expensive. If cost is a concern, a cheaper alternative is a basic scanner with a manual duplexing feature in its driver. This is a good choice if you only need to scan two-sided documents once in a while.
What operating system are you using? Pretty much any scanner works with recent versions of Windows, but if you're using a Mac or Linux system, double-check to make sure the scanner is compatible with it. We saw many complaints from Mac users who bought scanners only to discover that they weren't compatible with the latest version of the Mac OS – or, in other cases, with older versions.