javascript - image input type not being detected -

i trying submit form using image input type. ajax request performs fine, , response php script. problem want image button change it's image when submitted (and wasn't doing that). firebug console said form.pic undefined, , image not updated. ideas why?

javascript/jquery

function new_user(form){      var url = "attendance.php";      var datastring = "status="+form.astatus.value;     datastring = datastring+"&id="+form.mark_attend.value;     $.ajax({   type: "post",   url: url,  data: datastring,   success: function(data) { form.pic.src = data; //error here }, error: function(jqxhr, textstatus, errorthrown){ console.error("error: " + textstatus, errorthrown);} });  return false; } 

html

<form method="post" onsubmit="return new_user(this);" > <input type="hidden" value="attended" name="astatus" /> <input type="hidden" value="idkey" name="mark_attend" /> <input type="image" src="greencheck.png" name="pic" /> </form> 

$(form).find('input[name="pic"]').attr('src', data); 

this, think, cleanest way considering using jquery.