Three file types are supported by current browsers.

• GIF (also known as Compuserve GIF) - Graphic Interchange Format
• JPEG - Joint Photographic Experts Group
• PNG - Portable Network Format

GIF

GIF files are best used for images that have broad areas of flat color and are highly defined. One valuable feature is its support for image transparency.

• Keep files small
• Use flat colors
• Reduce the number of colors in the image
• Crop off extra space, if possible

JPEG

JPEG files are best used for images that blend many colors smoothly, such as photographs.

JPEG files are compressed with "lossy" compression. Some of the information in the file is lost at compression time and cannot be recovered. JPEG image quality is measured by a "Q" setting from 1 to 100. 100 is best.

PNG

PNG has been developed as an alternative to GIF. It has a lot of potential, but does not have broad-based browser support.

A Comparison between GIF and JPEG

Examine the two images below...
You should be able to see that the GIF image on the left is "rougher" than the JPG image on the right.

This effect was exaggerated for this example by reducing the GIFs color palette to only 16 colors.