The first decision you have to make when it comes to buying a photo printer is whether you want your printer to only make photos or, if it should accomplish other things as well. While multifunction printers may be convenient for the home office, they typically aren't going to provide the high-level photographic quality that's so easily attainable in dedicated photo printers. So, first off, choose a true photo printer—unless you absolutely need it to do double-duty in a home office.
Next up is another fundamental decision: what sort of photo printer technology would you like to subscribe to? This decision typically is answered in one of two ways: dye sublimation or inkjet. Dye-sub printers are commonly used for applications where a photographer needs to print a high volume of small prints very quickly. If you've ever been in a photo booth, or at an event where a print was handed to you on the spot, chances are good you've encountered a dye sublimation print. It probably looked fine, but I bet it didn't look great. For great photos, the choice is usually inkjet. If you're looking to start an instant-printing business, however, consider dye-sub.
Assuming you're going down the path of inkjet, the next question is exactly what kind of ink your printer is using. Dye-based inks were the original standard, and they produced bright, saturated, vivid colors—although they didn't last especially long and they weren't particularly durable. While vast improvements have been made to dye inks in both of those areas, another big change occurred when manufacturers started offering printers that worked with pigment inks. These pigment inks are designed to last for a long, long time—like hundreds of years long. They're practically permanent. The sacrifice is that they tend to not make prints quite as bold and vivid as dye-based inks. Both technologies produce outstanding prints, with great colors, that last a long time. But here's where personal preference starts coming into play: if you'd rather give the edge to long-lasting image permanence, go with a pigment ink. For vivid, in-your-face color, go with dyes.
Now it's time to decide just how big is big enough for you. Most photo printers (almost all of them, in fact) have no trouble printing a full bleed 8x10 or a letter sized 8.5x11-inch print. Many in the mid-range, though, step up their width to 13 inches. This makes it possible to make enlargements up to 13x19 (or even 13x44 panoramas) depending on the machine. Some high-end desktop units are 17 inches wide, which makes 16x20s a snap, and still larger printers can make posters easily attainable—if you've got the empty floor space and plenty of room in the budget. Generally speaking, the largest prints you can make from a desktop printer max out in that 17-inch range.
Not that you need to know exactly how an inkjet works, but I'll still explain the two subtle variations in technique. There's the thermal inkjet printer, in which ink is heated and a bubble is created that squeezes droplets out of the printhead. This is the technique used by Canon printers; remember that they used to be called bubble jets? Now you know why. The other technique is the piezoelectric printhead, which uses an electrical charge to spray inks in multiple droplet sizes. This is the technology used in Epson printers. While it's not quite as fast as thermal printheads (which frequently have more nozzles), the quality from each is tremendous.
Droplet size is measured in picoliters—which is one-trillionth of a liter. That's a small dot. Small is good, because in order to achieve the illusion of a continuous tone print you don't want to see any dots at all. It's not just size that affects this, though; it's how close together they're placed. In early inkjets with fewer inks, where lighter tones were needed the dots were simply placed farther apart. This made the dots themselves more distinguishable. But not only have inkjets advanced in terms of how small their droplets are and how closely together they can be placed, they've increased the number of inks to incorporate lighter tones as well. That means the droplets can be placed close together for a continuous tone effect even in lighter areas of the print.
If you're looking to produce black-and-white prints from your inkjet printer, you've got a few additional concerns. Seeking out a printer with additional inks that include at least a couple of versions of black and gray will allow you to rely solely on those grayscale inks to produce grayscale prints. It's when colored inks are combined to approximate gray that unwanted color shifts appear. But with multiple black and gray inks, the challenge is considerably simpler. Pair those inks with a great photo paper and you'll crank out prints that look an awful lot like those that used to come out of actual darkrooms.
And now, just a couple of printer suggestions. If you're serious about black-and-white printing, Canon's Pixma PRO-1 with its five gray and black inks is an ideal candidate. It also produces beautiful color images, but it really shows its ink advantage in black-and-white. For large-scale prints, Epson's Stylus Pro 3880 is about as big as you can get in a desktop printer, accepting sheets up to 17 inches wide. It's a very popular choice for photographers who want high quality and large output. Those two printers are at the top of any photographer's wish list, but rest assured that each manufacturer offers plenty of options in models well under the $1,000 mark as well.