One browser may display an image differently than another and computer monitors have different resolution settings and color depths. The smaller the graphic, the faster it will appear on a reader's screen. Smaller file size also means the image quality won't be as good as it would be for a printed image, but the typical computer monitor can't display an image as crisply as a printing press anyway, so the trade-off is acceptable. Images used on the Web are made up of small squares called pixels. The higher the resolution, the more pixels in the image.
Higher resolution allows for more detail and subtle color transitions in an image.
A printed image that has a low resolution may look pixelated or made up of small squares with jagged edges and without smoothness. Pixels per inch used to measure resolution or the density of a scanned image. Pixels are the small points of light that create the image on a computer monitor or television monitor. The more pixels, the sharper the image. Graphics on your monitor are made up of individual dots of color known as pixels.