// getElementsByClassName from http://www.robertnyman.com/2005/11/07/the-ultimate-getelementsbyclassname/
function hideBlankAds_getElementsByClassName(oElm, strTagName, strClassName){
    var arrElements = (strTagName == "*" && oElm.all)? oElm.all : oElm.getElementsByTagName(strTagName);
    var arrReturnElements = new Array();
    strClassName = strClassName.replace(/\-/g, "\\-");
    var oRegExp = new RegExp("(^|\\s)" + strClassName + "(\\s|$)");
    var oElement;
    for(var i=0; i<arrElements.length; i++){
        oElement = arrElements[i];      
        if(oRegExp.test(oElement.className)){
            arrReturnElements.push(oElement);
        }   
    }
    return (arrReturnElements)
}

// Search for tags with the class name "ad_content"
// If all images in the tag contain the string "empty.gif"
// then set style to display: none;
function hideBlankAds (className, imgString) {

	if (!document.getElementsByTagName) {
		//alert('browser incompat');
		return;
	}

	var ads = hideBlankAds_getElementsByClassName(document, "*", className);

	var foundSpacer    = false; // ad box has a spacer image
	var foundNonSpacer = false; // ad box has a non-spacer image

	var spacerRegExp = new RegExp(imgString);

	for (var i=0; i < ads.length; i++) {
		foundSpacer    = false;
		foundNonSpacer = false;

		var adImgs = new Array();
		adImgs = ads[i].getElementsByTagName("img");
		for (var j=0; j < adImgs.length; j++) {
			if (adImgs[j].src && !foundNonSpacer) {
				if (spacerRegExp.test(adImgs[j].src)) {
					foundSpacer = true;
				}
				else  {
					foundNonSpacer = true;
				}
			}
		}

		if (foundSpacer && !foundNonSpacer) {
			ads[i].style.display = "none";
		}
	}
}

hideBlankAds("ad_content", "empty.gif");