이 코드에서 이미지 중복을 정지하고 싶은데 어떻게 하나요..??

<tr id="topArea" width="1000px">			<div id="div_RotationImage" z-index="10" style="display: block; background: url(&quot;img/main_banner02.png&quot;); background-repeat:no-repeat; <!--width: 1000px; top: 0px; height: 596px;--> position: absolute;">			</div>			<script>				function rotationImage(){					document.getElementById("div_RotationImage").style.background = "url('" + rotationImageUrl[imagePointer] + "')"; 										if(imagePointer >= rotationImageUrl.length-1) imagePointer = 0; 					else imagePointer++;				}								var rotationImageUrl;				var loc = "";									switch(loc){						default:							rotationImageUrl= [							"img/main_banner01.png",							"img/main_banner02.png"							];						break;											}								var imagePointer = 0;								rotationImage();				if(rotationTopBg != null) clearInterval(rotationTopBg);				var rotationTopBg = setInterval("rotationImage()", 4000);			</script>		</tr>