One of the most common mistakes that people make when they are preparing images for print is that they incorrectly size their images. Making sure that your image's size and resolution match is one of the easiest ways to ensure that your project will look its absolute best.
When you are preparing pictures for publication, it is important to think about how it will be reproduced. The two different methods that I usually use are print and internet.
Images destined for the internet are simple. Computer screen images are made up of little red, green, and blue dots that are placed right next to each other. There are 72 rows of these dots per inch, and therefore a 72 dpi image is sufficient for the web, or any other graphic that stays on your computer.