"Optimizing" graphics usually refers to techniques you can implement using tools like Photoshop, Debabelizer, or Fireworks to get the best image quality at the smallest file size. While these techniques depend on image editing software, consider the following guidelines to make your images and sharp as possible without requiring a prohibitive file size.
Reduce the number of colors in your image as much as possible before a visible degradation occurs. Most graphics applications like Photoshop and Fireworks enable you to view different iterations of an image with fewer and fewer colors. Choose the one that reduces the file size the most while still looking sharp.
Crop your images as much as possible. This may seem like a no-brainer, but take a tour of a few sites and you're sure to find at least one image that could have been cropped more to reduce its size.
Use the right file type for the image.
In addition, there are several things you can do with HTML that will make your images and image-based designs more flexible and usable.