body::after{
position:absolute; width:0; height:0; overflow:hidden; z-index:-1;
content:url(img01.png) url(img02.png) url(img03.png) url(img04.png);
}
/* preloader */
div#preload {
display: none;
}
<!-- preloader -->
<div id="preload">
<img src="img/bg/BG1.jpg" width="1" height="1" alt="Image 01" />
</div>