[Plugin: Opengraph and Microdata Generator] Select Featured Image

the function iafbschema_image() get first image in post to set og:image tag.
In my blog i haven’t image in post but i set it manually in the code. If you want to get featured image instead of first image of the post change the funcion at row 166 of opengraph-microdata.php:

function iafbschema_image()
{
    if (has_post_thumbnail( get_the_ID() ) ):
		$image = wp_get_attachment_image_src( get_post_thumbnail_id( get_the_ID() ), 'single-post-thumbnail' );
		$image = $image[0];
	else:
		$Html = get_the_content();
		$extrae = '/<img .*src=["\']([^ ^"^\']*)["\']/';
			preg_match_all( $extrae  , $Html , $matches );
		$image = $matches[1][0];
	endif;
    if($image)
    {
		$pos = strpos($image, site_url());
		if ($pos === false) {
			return $_SERVER['HTTP_HOST'].$image;
		} else {
			return $image;
		}
    } else {
		return get_option('wpogmcthumbnail');
    }
}

http://ww.wp.xz.cn/extend/plugins/opengraph-and-microdata-generator/