Resolution is especially crucial for print design. The resolution of the image or graphics determines the quality of the final physical product.
Two terms factor into the resolution of your printed image — DPI and PPI. Although they are similar, each plays a different role. DPI, or dots per inch, is the density of ink within each inch of a printed surface. This term is most important during the actual printing process and means little for web design due to it coming into play once an image prints on to a surface. Equipment set to require greater DPI means a higher quality image.
PPI, or pixels per inch, is how many pixels are displayed each inch of screen space. The higher the number of pixels in an image, the better quality the image will be. Lack of pixels causes distortion, blurriness and overall loss of quality. PPI has an interesting relationship with how an image appears once it is in print. A higher number of pixels per inch condenses the size of a print but also increases the quality. So to see the best results, you must determine the correct PPI for the desired quality and quantity.
A good rule of thumb is to print at 300 PPI. This recommendation correlates with the maximum amount that the human eye can recognize, and as a result, will generally mean a quality physical image.