Web vs. Print Resolution
In regards to web vs. print resolution, one important thing you need to consider is the term PPI, or Pixels per Inch. People (including myself) tend to use the term interchangeably with DPI, or Dots per Inch. If you were to walk into a print shop right now and start throwing those words around, they will know what you’re talking about.
Technically speaking, however, DPI refers to the amount of ink (dots) your printer can fit onto an inch of paper. This number is usually a set range specific to each machine, and generally can’t be changed by the end-user. PPI, on the other hand, can refer to a couple of things. For example: computer monitors commonly have pixel densities that range between 72 to 96 PPI. High-density screens, like those found on retina iPhones, can go upwards of 400. In the context of this article, we’re discussing printing, so in this case PPI refers to the number of pixels that fit on an inch of paper. Any time you’re adjusting an image to be print-ready on your computer, you’re changing the PPI.
In all cases, though, a higher DPI or PPI always results in a crisper, higher quality image, and 300 PPI is the de facto standard for printing something to size. For those who wish to read more on the subject, check out this article at 99Designs, and this article at Digicam Guides.