How long your prints of digital images are going to last depends on the technology used to print them. That includes both ink and paper. Most people use inkjet printers to produce images, and two primary technologies are used. One is based on organic dyes, and the other is based on pigments. Loosely speaking, the first is like coloring your clothes, and the second is like painting your house.
The problem with organic dyes is that they fade. Your clothes fade with washing (and fade really fast if you hang them out in the sun to dry). Chemicals in the environment and ultraviolet radiation are the enemies of organic dyes. This is especially true for red dyes. You may have seen posters that have hung in the window of a store for a long time, and most of the colors other than blue have faded away. Finding a UV-stable red dye is the holy grail of commercial organic chemistry. Canon printers produce glorious output but do so using organic dyes, so they can't be counted on to last unless you keep them in the dark, and then, what's the point?
The paint on your house, however, can stand up to a lot of UV punishment. It tends to lose flexibility, and flakes off, before it loses much color. This is partly because paints use pigments rather than dyes. Epson has several pigment-based printers and estimates that they will produce output lasting for decades to centuries before there is significant loss of color. You might ask why everyone doesn't use pigments and one reason is that it is harder to prevent pigment-based inks from clogging the holes in the print head. Epsons, in fact, have something of a reputation for this problem.
You might also ask how anyone knows that a print will last a century when digital printing technology hasn't even existed for that long. Laboratories do accelerated aging tests -- for example, shine very bright UV light on an image for a short period of time, measure the effect, and extrapolate the results to ordinary situations using some sort of scaling assumptions. In other words, they don't really know. They have an educated guess, based on related data. Accelerated aging tests are something of a dark art, and Wilhelm Imaging Research is the leading wizard (http://www.wilhelm-research.com/). If you're looking for detailed information that is the place to look. But their tests are expensive and some companies aren't willing to pay the price.
It is also worth noting that ink is not the only factor in the equation. Ink sits on paper, and there is a complex and not fully understood chemical interaction between them. What we do know is that the longest lifetimes are obtained by using both ink and paper produced by the same company that made your printer. That also typically means the most expensive ink and paper, but there you go -- it is an interacting system of parts, not a whole bunch of separate and interchangeable pieces. According to Wilhelm, some of the recent HP's achieve lifetimes on the order of 60-70 years even though they use dye-based technology. But that is only for HP ink on HP paper.
So what do you, as a consumer, do? You can look at cNet's reviews but they will not reliably tell you what type of technology each printer uses (a systemic flaw, in my opinion). For what it is worth, the most frequently used printers among photography enthusiats seem to be Epsons, at least judging from their websites.
And also, for what it is worth, film photography has stability problems too. Fading of silver halide photographs was first studied by the Photographic Society of London, which set up its Fading Committee in 1855. The problems identified then have never been fully solved. Fading, then as now, is associated with the accumulation of sulfur compounds from environmental sources but also from the fixer (sodium thiosulphate) bath in photo processing, and careful, thorough washing is required. After proper archival processing, they can last centuries, but few commercial photolabs have ever taken such care with their processing. This is why your family pictures from the 1950's are probably already pretty badly faded.
Color photography is even worse since it involves the use of (yet again!) photosensitive organic dyes. If you keep color photographs stored in a dry, dark chamber at a constant zero degrees Fahrenheit, you can hope to get about 50 years out of a color photo. If you hope to look at them from time to time, lifetimes will be correspondingly shorter. This is why Kodak prints, in bright Kodak yellow on the side of every box of color film: Since color dyes may change over time, this product will not be replaced for, or warranted against, any change in color. You can see some examples of faded (and restored) color photographs here:
Kodachrome is thought to be the most stable color film, but "burning in (whatever that is)" has little to do with it. It is dye chemistry, pure and simple, and always has been, since the Fading Committee first studied the problem.
Submitted by: Paul C. of Atlanta, GA