“Have you ever asked to your client “What resolution do you want it?” he responds, “Make it 300 DPI”(dots per inch). Video and 3D Animation work in Pixels. Many times, animators render out a 3000 by 2000 pixel image, bring it into their imaging program, and it reads 72 dpi. This is inaccurate…”
http://www.cgarena.com/freestuff/tutorials/72or300dpi/72or300.html