(from www.microsoft.com/windowsxp/using/digitalphotography/takeit/default.mspx)
The sensor in a digital camera is composed of pixels, which are tiny light-sensitive squares. The sensors in most cameras today are made up of millions of pixels, each one registering the brightness of the light striking it as the photo is taken. The number of pixels in the image is about equal to the number of pixels on the sensor. This number is referred to as the image's resolution. Simply put, the greater the number of pixels in an image, the higher the resolution. And the higher the resolution, the better and larger the print you can make from your computer and printer. Put nother way, resolution affects the output options for your photo. It's important to keep this in mind as you explore the resolution options on your camera.
Most digital cameras allow you to change the resolution setting, so you can fit more or fewer images on your memory card. This can be a helpful feature if you only have one card or if you re on a trip and can't transfer photos to your computer. But if you take a photo of a spectacular sunset, and you capture it on a lower resolution setting like 800x600, you may be unhappy with the result if you want a 5x7 or 8x10-inch print. That's because the low resolution image lacks detail, and may also appear jagged. Carrying additional memory cards and keeping the camera set on its highest resolution setting is a better solution.
The higher the photograph's resolution, the more plentiful printing and sharing options exist. With this in mind, the best bet is to shoot photos at the highest resolution your camera can capture. The resolution can easily be adjusted downward on your computer - when you're sending photos by e-mail, for example. However, there is a limit to how effectively photo resolution can be adjusted upward by a computer. This means, for example, you can always make a sharp, clear, small print from a high-resolution photo, but you can't make a rich, detailed, large print from a low-resolution one.
Resolution does dictate the maximum print size you can expect from a camera. In general, a 2-megapixel camera will produce a good 4 x 6-inch image using a typical desktop colour inkjet printer. With a 3-megapixel camera, you can turn out a very good 8 x 10-inch print, which is the largest print anyone not a professional is likely to need.
However, if you print only one photo out of a hundred, do you still want to take pictures in high resolution-just in case you get one that cries out to be printed? Or what if you can't be bothered changing the scanner's resolution every time you scan in a photo? That great resolution you paid extra for is excessive for photos that are only going to be seen on a computer monitor.
If your pictures are destined for e-mail or a Web site, lower the resolution by changing the setting on your camera. Most digital cameras can be set to take pictures described as Good, Better, Best, or some variation on that. To see exactly what resolution each setting represents, consult the camera's user manual and try the different settings. Determine how low a resolution you can set that still results in good-looking pictures.