div {
    width: 600px;
    height: 600px;
    background: 
    url(../img/bgimage1.jpg) no-repeat top left,
    url(../img/bgimage-2.jpg) no-repeat top right,
    url(../img/bgimage-3.jpg) no-repeat bottom left,
    url(../img/bgimage-4.jpg) no-repeat bottom right;
}
.div {
    width: 1000px;
    height: 1000px;
    background: 
    url(https://picsum.photos/id/237/300/300) no-repeat top left/50%,
    url(https://picsum.photos/id/238/300/300) no-repeat top right/50%,
    url(https://picsum.photos/id/239/300/300) no-repeat bottom left/50%,
    url(https://picsum.photos/id/240/300/300) no-repeat bottom right/50%;
}