<table>
    <tr>
        <td id="3">
            <a href="#" class="thumb">
                <img class="thumbimg" src="images/image1.png" alt="image1.png" />
            </a>
        </td>
    </tr>
</table>
<script type="text/javascript">
            $('.thumbimg').click(function () {
                imgID = $(this).closest('td').attr('id');

                var newSrc = imgPath + $(this).attr('alt');
                mainImage.attr('src', newSrc);

                $('#gallery').attr('width', mainImage.attr('width') + '15px');
            });
</script>