My image is 72 dpi, is that ok?
NO. Most web graphics are 72 dpi which is not a problem. But when it comes to printing, the images or files that you submit must be 300 dpi, at final size, to ensure maximum sharpness and quality. Failure to do so may result in pixelation and blurriness in the final product.
Beware of Interpolation!
DO NOT interpolate! Here's the scenario. You created your files at a low resolution (ex: 72 or 150 dpi) and then you manually go and change the resolution to 300dpi. This results in asking the computer to calculate the pixels that are not there and to add new ones, thereby interpolating the image. Computers cannot add new data to sharpen the image, they can only add "filler" pixels. This usually always results in blurry and muddy images. Hence, if your original file was created at anything less than 300 dpi, it IS NOT acceptable to simply go and manually change the resolution to 300 dpi after the files have been created. Your files or images must be either recreated or rescanned at 300 dpi. Please remember that the image or file needs to be 300 dpi at FINAL SIZE. So if an image is 2"x2" at 300 dpi and then placed in a page layout program, such as Quark Express, and blown up 200% to 4x4", the resolution now is only 150 dpi. Please watch out for this pitfall.