You can use multiple backgrounds if there is no transparency involved and they occupy all available space or have the same size:
div{
background-image: url('http://placehold.it/1000x1000'), url('http://placehold.it/500x500');
background-repeat:no-repeat;
background-size: 100%;
height:200px;
width:200px;
}
<div></div>
If the first doesn’t exit, the second will be displayed.
div{
background-image: url('http://placehol/1000x1000'), url('http://placehold.it/500x500');
background-repeat:no-repeat;
background-size: 100%;
height:200px;
width:200px;
}
<div></div>