html, body {
    width: 100%;
    height: 100%;
    background: url('bg-image2.jpg') center no-repeat;
    background-size: cover;
    background-attachment:fixed;
}

.parent {
    width: 100%;
    height: 100%;
    position: fixed;
    top: 0;
    left: 0;
    display: flex;
    align-items: center;
    align-content: center; 
    justify-content: center; 
    overflow: auto;   
}

.parent img {
    display: block;
    border: none;
    width: 30%;
    max-width: 400px;
}

#mask {
    background-color:rgba(0,0,0,.5);
    height:100%;
    position:fixed;
    width:100%;
    top:0;
    left:0;
}

@media screen and (max-width: 1024px) {
    .parent img {width: 70%; max-width: 500px;}
}