Código PHP:
<?php
$img=glob("./screenshots/*.jpg");
$f="./screenshots/" .$_GET[Screenshot]. ".jpg";
$t = str_replace("-", " ", $_GET[Screenshot]);
echo "<h1 align='center'>$t</h1><br>";
echo "<a href='$f'><img width='400px' border='0' height='300px' src='$f'></a>";
echo '<br><a href="Imagenes.php?Screenshot='.implode($img).'"><img width="100px" height="80px" border="0" src="'.implode('"> <img width="100px" border="0" height="80px" src="',$img).'"> </a>>';
?>