First i have to become familiar with adding and updating a plugin on Wordpress via subversion.tigris.org
I did a litle update because, the plugin is called when the get_header in your theme is called and is in a single page. previously it was called in the footer but one of my theme didn't have get_footer in the template.
I see it's version 0.1 but it suposed to be 0.2
if it did not updated edit the plugin and just replace
add_action( 'wp_footer', 'gc_featured_img' );
by
add_action( 'get_header', 'gc_featured_img' );
Give your feedback here :)
