Featured image Open Graph meta tag

gistfile1.aw

<?php
function canvas_featured_open_graph_meta() {
    if ( is_single() || is_page() ) {
    	global $post;

        if ( has_post_thumbnail( $post->ID ) )
            $thumbnail_id = get_post_thumbnail_id( $post->ID );

        if ( ! empty( $thumbnail_id ) ) {
            $thumbnail_src = wp_get_attachment_image_src( $thumbnail_id );

            echo '<meta property="og:image" content="' . esc_url( $thumbnail_src[0] ) . '" />';
        }
    }
}
add_action( 'wp_head', 'canvas_featured_open_graph_meta' );