Shirt-Creator

HTML

<script type="text/javascript">
    function changePattern(a) {
        document.getElementById("pattern").src = a;
    }

    function changeStyle(a) {
        document.getElementById("style").src = a;
    }
</script>
<div id="main_img">
    <img id="pattern" src="http://us.123rf.com/400wm/400/400/davorr/davorr1101/davorr110100011/8627355-pilze-seamless-pattern-swatch-muster-included-in-eps-datei.jpg" width="400" height="400" />
    <img id="style" src="https://dl.dropboxusercontent.com/u/62849616/Stackoverflow/shirts/hemd.gif" width="400" height="400" STYLE="position:absolute; TOP:8px; LEFT:8px" />
</div>
<div id="thumb_img">
    <img src='http://us.123rf.com/400wm/400/400/davorr/davorr1101/davorr110100011/8627355-pilze-seamless-pattern-swatch-muster-included-in-eps-datei.jpg' onclick='changePattern("http://us.123rf.com/400wm/400/400/davorr/davorr1101/davorr110100011/8627355-pilze-seamless-pattern-swatch-muster-included-in-eps-datei.jpg");' width="80" height="80" />
    <img src='http://www.kloth.org/images/muster23.gif' onclick='changePattern("http://www.kloth.org/images/muster23.gif");' width="80" height="80" />
    <img src='http://us.123rf.com/400wm/400/400/studiom1/studiom11102/studiom1110200793/9131199-beratung-seamless-vektor-muster-mit-wort-wolke-abbildung-mit-verschiedenen-association-bedingungen.jpg' onclick='changePattern("http://us.123rf.com/400wm/400/400/studiom1/studiom11102/studiom1110200793/9131199-beratung-seamless-vektor-muster-mit-wort-wolke-abbildung-mit-verschiedenen-association-bedingungen.jpg");' width="80" height="80" />
    <br>
    <img src='https://dl.dropboxusercontent.com/u/62849616/Stackoverflow/shirts/hemd.gif' onclick='changeStyle("https://dl.dropboxusercontent.com/u/62849616/Stackoverflow/shirts/hemd.gif");' width="80" height="80" />
    <img src='https://dl.dropboxusercontent.com/u/62849616/Stackoverflow/shirts/tshirt.gif' onclick='changeStyle("https://dl.dropboxusercontent.com/u/62849616/Stackoverflow/shirts/tshirt.gif");'...