in the galleries/ribbon_fullsize_lightbox/index.php file, the ribon is created by the following code:
<!-- ribbon -->
<div class="ribbon">
<div class="prev"></div>
<div class="thumbs-wrapper">
<div class="thumbs">
<div class="thumbs-ribbon-scroller" >
<?php if(sizeof($gallery['images']) <= 0) { ?>
<div class="no-images">no images</div>
<?php } ?>
<?php
for($i = 0; $i < sizeof($gallery['images']); $i++) {
echo '<img alt="" title="' . $i . '##' . str_replace('"', '\"', $gallery['images'][$i]['title']) . '##' . str_replace('"', '\"', $gallery['images'][$i]['description']) . '" src="' . $gallery['images'][$i]['thumb']['url'] . '" width="62" height="62" />';
}
?>
</div>
</div>
</div>
<div class="next"></div>
</div>
removing that code will remove the ribon.
NOTE:
This is not a supported modification.
Removing the ribbon may break other functionality.