$(function () {

    for (var i = 0; i < images.length; i++) {
        $("<img>").attr("src", images[i]);
    }

    $(".preview")
    .hover(
        function () {
            var backgroundImage = $(this).css("background-image");
            if (backgroundImage.indexOf("grayscale") >= 0) {
                $(this).css("background-image", backgroundImage.replace("thumbnails/grayscale", "thumbnails"));
            }
        },
        function () {
            var backgroundImage = $(this).css("background-image");
            if (backgroundImage.indexOf("grayscale") == -1) {
                $(this).css("background-image", backgroundImage.replace("thumbnails", "thumbnails/grayscale"));
            }
        }
    );

});