如果要使用该函数在某处输出代码：

function displayImage($currentPost) {

    // Show the featured icon only if current post is in "featured" category
    if ( in_category ( \'featured\', $currentPost ) ) {

        $output = \'<a href="<?php the_permalink(); ?>">
                            <span  class="featured_icon">
                                <img src="<?php bloginfo(\'template_directory\'); ?>/images/featured_icon.png" />  
                            </span>
                      </a>\';
    }

    else { $output = \'\' };
    return $output;

}