Atualize essa pagina / Pressione F5 / para trocar a image de fundo

COMO FAZER UMA TELA COM BACKGROUND DINAMICO IGUAL A ESSA:
		
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	function ini(){		
		f_teste("fundo10.jpg","fundo17.jpg","fundo23.jpg","fundo14.jpg","fundo16.jpg","fundo19.jpg","fundo22.jpg","fundo24.jpg","fundo25.jpg","fundo26.jpg","fundo32.jpg","fundo34.jpg","fundo41.jpg","fundo42.jpg","fundo43.jpg",	"fundo45.jpg","fundo47.jpg","fundo48.jpg","fundo49.jpg","fundo52.jpg","fundo54.jpg","fundo58.jpg","fundo63.jpg","fundo67.jpg","fundo72.jpg","fundo73.jpg","fundo74.jpg","fundo79.jpg","fundo81.jpg","fundo83.jpg","fundo84.jpg", 	"fundo85.jpg","fundo89.jpg","fundo90.jpg");
	}

	function f_teste(){	
		var a=f_teste.arguments; 
		var tam = a.length - 1;
		anterior = indice;
		indice = randomIntFromInterval(0,tam);
		while(indice==anterior){
			indice = randomIntFromInterval(0,tam);
		}
		var el = document.getElementById("idDivBackgroundRandomico");
		el.style.backgroundImage="url('img/" + a[indice] + "')";
		el.style.backgroundRepeat = "repeat-x";
		el.style.backgroundSize = "1980px 100%"
		el.style.position = "absolute";
		el.style.top = "0";
		el.style.left = "0";
		el.style.width = "3900px";
		el.style.height = "100%";
		el.style.zIndex = "-9999";
		el.style.opacity = "0.9";
		
		document.getElementById("span-nome-da-imagem-id").innerHTML = a[indice];
	}

	function randomIntFromInterval(min,max){
		return Math.floor(Math.random()*(max-min+1)+min);
	}	
	
	<html>
		<body onload="ini()" id="body_id">
			<div id="idDivBackgroundRandomico"></div>
		</body>
	<html/>

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