GIF files should be used for graphics, line art and simple color images . JPEG should be used for photographic images, complex colors, full color images or for images that contain a graduated range or blend of colors. The physical dimensions of the image. This is generally expressed in units of measure such as inches, or by pixels. A pixel is one dot on a computer or video monitor screen.
Resolution is also a parameter of laserprinters.
Most laserprinters have a resolution of 300 or 600 dpi. It affects download time on the Web, and affects printing time to a laserprinter. Larger files take longer to download and longer to print. You need to balance all of the criteria in determining how to create and save your file. File size is how large the file is as expressed in bytes of data.