George616 says:

                <script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>

                <link rel="stylesheet" href="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.24/themes/start/jquery-ui.css" />

                <script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.24/jquery-ui.min.js"></script>

                <script type="text/javascript">

                    $(function () {

                        $("#dialog").dialog({

                            autoOpen: false,

                            modal: true,

                            height: 400,

                            width: 410,

                            title: "Zoomed Image"

                        });

                        $("[id*=GridView1] img").on('mouseenter', function () {

                            $('#dialog').html('');

                            $('#dialog').append($(this).clone());

                            $('#dialog').find('img')[0].style.width = '375px';

                            $('#dialog').find('img')[0].style.height = '350px';

                            $('#dialog').dialog('open');

                        });

                    });

                </script>

Since you are using multiple version of jQuery there is Conflict and error.

So you have to use noConflict function to allow multiple versions work together without conflicting.

Replace above with below code to use multiple version of jQuery.

<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<link rel="stylesheet" href="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.24/themes/start/jquery-ui.css" />
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.24/jquery-ui.min.js"></script>
<script type="text/javascript">
    var $j = $.noConflict(true);
</script>
<script type="text/javascript">
    $j(function () {
        $j("#dialog").dialog({
            autoOpen: false,
            modal: true,
            height: 400,
            width: 410,
            title: "Zoomed Image"
        });
        $("[id*=GridView1] img").on('mouseenter', function () {
            $j('#dialog').html('');
            $j('#dialog').append($(this).clone());
            $j('#dialog').find('img')[0].style.width = '375px';
            $j('#dialog').find('img')[0].style.height = '350px';
            $j('#dialog').dialog('open');
        });
    });
</script>

For more details refer below article.

jQuery noConflict: Using multiple jQuery versions on the same page