anchor.diff:  			  Object temp1 = session.getAttribute("coursesInfo");
   			  course = (ArrayList<CourseInfo>) temp1;
   			  String cname = course.get(0).getCname();
  -			  String urlpic = (String)session.getAttribute("classPicUrl");%>
  +			  url = (String)session.getAttribute("classPicUrl");%>
   			
   			document.getElementById("courseTeancher").innerHTML= str;
  -			var bgurl = '"url('+<%=urlpic%>+')"';
  +			var bgurl = '"url('+<%=url%>+')"';
   			if(bgurl==null){
   				document.getElementById("bgurl").innerHTML="还未开始点名或者图片上传不成功，请耐心等候";
   				}else{
  
positive.code: 
  <script type="text/javascript">
  //声明Pic对象
  var id;
  var name;
  var size = 0;
  
negative.code: 		document.getElementById("stuname").innerText=name;
  		
  		var canvas = document.getElementById('myCanvas');
  		if (canvas.getContext && count == 1) {
  			var ctx = canvas.getContext('2d');
  
  			ctx.strokeStyle = '#0000ff';
  