Bagaimana menambahkan script input gambar pada function ajax ?

gimana cara untuk menginput gambar di fungsi ajax, saya bingung script gimana dan taruh dimana, please tolongin agan2 sekalian :D

//FILE TEACHERADD.PHP//

function AddTeacher(){

	if ( (document.addteacher.username.value=='') || (document.addteacher.fullname.value=='') || (document.addteacher.password.value=='') )  {
		sweetAlert("Oops...", "Harap Isi Field!", "warning");

	}
	else
	{

	var ajaxRequest;  // The variable that makes Ajax possible!

	try{
		// Opera 8.0+, Firefox, Safari
		ajaxRequest = new XMLHttpRequest();
	} catch (e){
		// Internet Explorer Browsers
		try{
			ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
		} catch (e) {
			try{
				ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
			} catch (e){
				// Something went wrong
				alert("Your browser cannot support AJAX!");
				return false;
			}
		}
	}
	// Create a function that will receive data sent from the server
	ajaxRequest.onreadystatechange = function(){
		if(ajaxRequest.readyState == 4){

			var ajaxDisplay = document.getElementById('Result');
			if (ajaxDisplay.style.display == 'none') {
			ajaxDisplay.style.display = 'block';
			}

			ajaxDisplay.innerHTML = ajaxRequest.responseText;

			/*
			setTimeout(function() {
    		$('#Result').fadeOut('slow');
			}, 3000);
			*/

		}
		else
		{
			var ajaxDisplay = document.getElementById('Result');
			if (ajaxDisplay.style.display == 'none') {
			ajaxDisplay.style.display = 'block';
			}
			ajaxDisplay.innerHTML = "<img src=images/loading_bar.gif>";
		}
	}


	//gathers all the variables
	var username = document.getElementById('username').value;
	var fullname = document.getElementById('fullname').value;
	var password = document.getElementById('password').value;
	var gender = document.getElementById('gender').value;
	var position = document.getElementById('position').value;
	var subject = document.getElementById('subject').value;
	var level = document.getElementById('level').value;
	var active = document.getElementById('active').value;

	var queryString = "?username=" + username + "&fullname=" + fullname + "&password=" + password + "&gender=" + gender + "&position=" + position + "&subject=" + subject + "&level=" + level + "&active=" + active;

	//alert(queryString);

	ajaxRequest.open("GET", "sa_teacheradd_ajax.php" + queryString, true);
	ajaxRequest.send(null);

	}
}

-->
</script>

// FILE TEACHERADDAJAX.PHP //

<?php
session_start();
require_once "sa_login_class.php";
 $login = new Login();
 $login->koneksi();

if($login->cek_login())
{
//check availability of username
$sql="SELECT * FROM teachers WHERE username='".$_GET['username']."'";
$result=mysql_query($sql);
$numresult=mysql_num_rows($result);

if ($numresult>0) {
echo "<br><font class='fb4'>Username has already exist...</font><br><br>";
}
else
{

		  //inserting a record
        $sql="INSERT INTO teachers (
			  `username`,
			  `password`,
              `fullname`,
              `gender`,
              `position`,
			  `subject`,
			  `level`,
			  `school`)
              VALUES (
              '" . $_GET['username'] ."',
			  '" . $_GET['password'] ."',
			  '" . mysql_real_escape_string($_GET['fullname']) ."',
              '" . $_GET['gender'] ."',
              '" . $_GET['position'] ."',
			  '" . $_GET['subject'] ."',
			  '" . $_GET['level'] ."',
			  '" . $_SESSION['sc'] ."')";

//echo $sql;

$result=mysql_query($sql);
if ($result) echo "<br><font class='fb4'>Data has been added successfully...</font><br><br>";

}

}
?>