 <blockquote> <p>Themes have to declare their support for post thumbnails before the interface for assigning these images will appear on the Edit Post and Edit Page screens. They do this by putting the following in their functions.php file:</p> <p><code>add_theme_support( 'post-thumbnails' );</code></p> </blockquote> <p>Source: <a href="http://codex.wordpress.org/Post_Thumbnails#Enabling_Support_for_Post_Thumbnails" rel="nofollow">http://codex.wordpress.org/Post_Thumbnails#Enabling_Support_for_Post_Thumbnails</a></p>