New in WordPress 2.9: Post Thumbnail Images « Mark on WordPress
http://markjaquith.wordpress.com/2009/12/23/new-in-wordpress-2-9-post-thumbnail-images/

WordPress 2.9: Post Thumbnail Images

I should try to use this feature.

add_theme_support( 'post-thumbnails' );

What if you want to use a small 50×50 hard-cropped image for the home page, but want to use a 400 pixel-wide (unlimited height) image on the post’s permalink page? You’re in luck. You can specify additional custom sizes!