Random (Background) image

give a unique ID to your color-section – here in my case it was: randomized
this is for only one page of mine so there is the is_page conditional.
upload the images via ftp into a given folder ( here it is a folder on uploads-folder: random-images
then put only the image-filenames into the array.

function randomize_bg_image() {
if(is_page(34024)){ 
?>
<script type="text/javascript">
(function($){
	    var images = ['o2-7.jpg', 'o2-1.jpg', 'o2-2.jpg', 'o2-3.jpg', 'o2-4.jpg', 'o2-5.jpg', 'o2-6.jpg'];
	    $('#randomized').css({
	    	'background-image': 'url(/wp-content/uploads/random-images/' + images[Math.floor(Math.random() * images.length)] + ')'
	    });
})(jQuery);
</script>
<?php
}
}
add_action( 'wp_footer', 'randomize_bg_image' );

see: https://webers-testseite.de/bg-scheduling/