Typically the largest image you would want to display on a web page is 600 x 400 pixels. Using default settings an image of this size would be about 240 KB, many times larger than our target file size. First rule to consider in making an image is keep the dimensions small. One way to accomplish this goal is to crop the image to include only information that is pertinent. Fancy borders and excess image size cause files to be larger than needed.
Resolution is a measure of how sharp an image is or the amount of detail included in the file.
In computer terms this is described as pixels per inch. A pixel is a picture element or the smallest defined portion of an image. Typical computer resolution is 72 ppi. Print and photographic resolutions are much higher than this mark. The web is not capable of displaying ultra-high resolution images.