How to use custom pictures to display checkbox in Html

<label  for="agree" >              
        <img  class="checkbox" alt="选中" src="../img/checked.png" id="checkimg" onclick="checkclick();">   
     </label>      
     <input type="checkbox"  style="display:none" id="agree" checked="checked">   
     <script>   
         function checkclick(){   
            var checkimg = document.getElementById("checkimg");   
            if($("#agree").is(':checked') ){   
                $("#agree").attr("checked","unchecked");   
                checkimg.src="../img/unchecked.png";   
                checkimg.alt="未选";   
            } else{   
                $("#agree").attr("checked","checked");   
                checkimg.src="../img/checked.png";   
                checkimg.alt="选中";   
            }   
        }   
    </script>