水煮鱼的微信机器人不错，http://blog.wpjam.com/project/weixin-robot/

但是这个微信机器人如果你用ngg，那么显示图片会有点问题，做如下修改，会显示图片。

if(!function_exists('get_post_first_image')){
	function get_post_first_image($post_content){
		global $post, $wpdb;
		preg_match('@\\
no images were found
@i', do_shortcode($post_content), $matches);
		if($matches){	 
			$picture_id = $matches[1];
			$sql="SELECT * FROM {$wpdb->prefix}ngg_pictures p left join {$wpdb->prefix}ngg_gallery g on p.galleryid=g.gid  WHERE p.pid = ". intval( $picture_id ) . " ORDER BY sortorder, pid ASC";
			$ngg_image = $wpdb->get_row( $sql );
			return get_site_url()."/".$ngg_image->path."/thumbs/thumbs_".$ngg_image->filename;
		}else{
			return false;
		}
	}
}

有问题请留言。