var type = 'jpg'; // image TYPE
var url = 'images/'; // image Pass
function ChgImg(name,flg){
if(flg=="on"){document.images[name].src = url+name+'_on.'+type;
}else if(flg=="ov"){document.images[name].src = url+name+'_ov.'+type;
}else if(flg=="of"){document.images[name].src = url+name+'_of.'+type;
}
}