@helper ShowProductAdditionImageThumbnail(string additImageName)
{
var imagePath = @"~/Images/AdditionThumbnailImages/" + additImageName + "_thumb.jpg";
if (!File.Exists(Server.MapPath(imagePath)))
{
imagePath = "~/AdditionThumbnailImages/noThumb.jpg";
}
<img src="@Href(imagePath)" alt="Product Image"/>
}

// Addition image thumbonail
<div class="col-md-6">
    <ul id="productsList">
    @foreach (var item in productAdditImage) {
        <li>
            <div id="gallery">
                <figure>
                    <a href="/AdditionImageDetail/@item.addProductImageID">@Products.ShowProductAdditionImageThumbnail(@item.addImageName)</a>
                    <figcaption>                                                    
                        <a href="/AdditionImageDetail/@item.addProductImageID"><h4>Арт.&nbsp;@item.addImageName&nbsp;</h4> </a>                                                  
                    </figcaption>
                </figure>
            </div>       
        </li>
}
    </ul>
</div>

}

<div id="photo">
        <p>@Products.ShowProductAdditionImage(@additImage.addImageName)</p>
    </div>

<script>
        $('#gallery a').click(function (evt)
        {
            evt.preventDefault(); // предотвращаем переход по ссылке
            var imgPath = $(this).attr('href');
            var oldImage = $('#photo p');
            var newImage = $('<img src="' + imgPath +'">');
            newImage.hide();
            $('#photo').prepend(newImage);
            newImage.fadeIn(1000);
            oldImage.fadeOut(1000, function ()
            {
                $(this).remove();
            });
            $('#gallery a:first').click();
        }); // End click
</script>