Image Formats
Images are usually saved in either JPEG (Joint Photographic Experts Group) or GIF (Graphic Interchange Format). By choosing the best format, you can create a web graphic that will download faster and look better.

The JPEG format works best for photographs. Adjust the size of the image in a photo editing program before adding to webpage. Save for web or save at 72 dpi (dots per inch).

The GIF format works best for graphics with solid areas of color, such as logos.
It is less efficient than the JPEG format at compressing complicated pictures with many colors and complex textures. The GIF file format allows images to be saved with transparent backgrounds.

Image Parameters
When adding images to web pages, always use the ALT parameter. The ALT parameter allows you to add a text description to an image that can be seen by users who are browsing with images turned off and also by web users who are using a voice reader.