a list element:
<a href="javascript:void();" onClick="javascript:prev(\''.$c['name'].'\')"><img src="gfx/photos/'.$c['name'].'" height="50" class="thumb"></a>

the preview:
<img id="pic" src="gfx/photos/'.$c['name'].'">

the script:
<script language="javascript">
function prev(name)
{
pic.src='gfx/photos/';
pic.src+=name;
}
</script>