LORENZO WINFREY has written an interesting article “How To Optimize Images For Your Website, WordPress Specific Tips Too” on Zoknowsgaming.
“Image optimization and compression is something that you should do to any image you are going to upload to your website, a good program can allow you to drastically shrink the actual size of the image but maintain its original image quality. ”
The article discuss a plugin called WP Smush.it that reduces image file sizes and improves performance using the Smush.it API within WordPress.
More: http://zoknowsgaming.com/2011/02/13/optimize-images-website-wordpress-specific-tips/