Unlike document scanners, photo scanners, good ones anyway, require impeccable color accuracy and high resolution. In fact, higher-end photo scanners also capable of scanning negatives, film, and 35mm slides support up to 6,000 dots per inch (dpi) and beyond. Scanning images that small at super high resolutions allows you to enlarge them without degrading the quality of the scans.
In addition, most photo scanners, again unlike document scanners, don’t come with automatic document feeders (ADFs) for scanning multiple pages automatically; although, some higher-end photo scanners do have add-on ADFs, and many have the ability to scan multiple images in a single scan. Some higher-end photo scanners come with adaptors for scanning transparencies, slides, film, and negatives.
Finally, if you’re scanning content for the Web or otherwise viewing on computer and mobile device screens, you really don’t need a high-resolution scanner, since monitors don’t display resolutions higher than 96 pixels per inch (ppi), which is the ppi of an HD monitor. Which brings up another issue: when scanning for online viewing, most (if not all) scanners nowadays will let you scan at ppi, rather than dpi. (Oh yes, I realize these are all Epson. Still waiting for others…)