Web designers are often asked “what DPI do you need?” when clients provide digital imagery for their websites. The best answer is coy and not well-accepted: “it does not matter.”
The Myth: DPI tells us the quality of an image.
DPI refers to “dots per inch”. It is a measure of print. Technically, DPI is a property of the image file that indicates nothing about the quality or resolution of the image. DPI exists to direct a printer how close to place the dots on the page. You can create a very high DPI file with very low image quality, and vice versa.
“Please move that box up so the page does not scroll.” The web designer then reaches for his canned “everyone will see this differently…” response. The term above the fold comes from print, where desktop publishers and editors can reliably determine priority placement for best content. The notion holds on the web: the designer needs to make the right impression above the scroll line. The problem is determining that point. And when you play it safe, cater to where you imagine it to be and leave some margin for error, you handcuff your design, and you’ll probably still get it wrong. 
