Printer resolution is the number of ink dots printed on an inch of paper measured in DPI (dots per inch). Most of today's printers have a resolution of 300 or 600 DPI. In most cases, the printer's resolution will not affect how you size and scale images. If you pick a template in FotoFinish or print your image at its actual size in inches, printer resolution will never effect the size of your printed image.
If you want to control the quality of your printed image for a professional result such as an image destined for publication in a newspaper or magazine, you can calculate the optimal resolution for your image based on a printer's LPI (lines per inch).
For most printers there is an optimum image resolution, beyond which increasing the embedded resolution of the image (PPI) makes no discernible effect on the output quality. Each printer can only print so many lines per inch (LPI). LPI measures the number of halftone dots a printer can create in an inch of paper. Halftone dots are how a printer simulates continuous shades of colors while only using four colors: cyan, magenta, yellow, and black (some photo-quality printers also add light cyan and light magenta). Every individual pixel in your image will be represented by a random pattern of these smaller, various-sized printer dots. This process is also called screening or halftoning.
Below are some common LPI outputs from different printers:
To obtain a quality print, your image resolution should be slightly higher than the printer's given LPI. To calculate this ideal resolution, multiply the LPI by about 1.5 to obtain the ideal pixel per inch (PPI) for your image. For example, for a 360 DPI photo-quality inkjet printer with a 150 LPI, you can get a photo-quality print if your image has at least 150 x 1.5 or 225 PPI.
If you don't know your printer's LPI, or if doing all this math seems too confusing, the best way to find your optimal print resolution is to experiment. Print a test image at various resolutions to find out what your minimum PPI is for a photo-quality print. A good test image is a close up picture of a newspaper or a photo that has some angled straight edges in it.