body {
    background-image: url('../images/background.jpg');
    background-repeat: no-repeat;
    background-attachment: fixed;
    background-position: bottom;
    background-size: cover;
}

img {
    position: absolute;
    top: 40%;
    left: 50%;
    width: 400px;
    height: 400px;
    margin-top: -200px; /* Half the height */
    margin-left: -200px; /* Half the width */
}