source: extensions/Media_Icon/include/thumbnails.inc.php

<?php
add_event_handler('loc_end_index_thumbnails', 'media_icon_thumbnails');

function media_icon_thumbnails($tpl_thumbnails_var) {
        global $template, $conf;

        $conf_media_icon_general = unserialize($conf['media_icon_general']);
        $conf_media_icon_advanced = unserialize($conf['media_icon_advanced']);
        
        $template->set_prefilter('index_thumbnails', 'media_icon_prefilter_thumbnails');
        
        $template->set_filename('media_icon_template', MEDIA_ICON_ABSOLUTE_PATH.'template/media_icon.tpl');
        
        $template->assign('media_icon_style',$conf_media_icon_general['style']);

        $template->assign('media_icon_active',  $conf_media_icon_general['active']);
        $template->assign(
                'media_icon_advanced',
                array(
                        'xposition' => $conf_media_icon_advanced['xposition'],
                        'yposition' => $conf_media_icon_advanced['yposition'],
                        'opacity' => $conf_media_icon_advanced['opacity'],
                )
        );
        
        $template->concat('PLUGIN_INDEX_CONTENT_END', $template->parse('media_icon_template', true));
        
        return $tpl_thumbnails_var;
}

function media_icon_prefilter_thumbnails($content) {
        global $template;
        
        $search = 'class="thumbnail"';
        
        $replacement = 'class="thumbnail" media_icon="{$thumbnail.file}"';
        $content= str_replace($search, $replacement, $content);

        return $content;
}
?>