jquery ajax post图片流给服务器进行图片上传

//ajax 上传
$("#upload").click(function(){
var url = "http://*mm.**com/ajaxupload.php";

var formData = new FormData($( "#frm" )[0]);
$.ajax({
url: url,
type: 'POST',
data: formData,
async: false,
cache: false,
contentType: false,
processData: false,
success: function (returndata) {
var jsonObj = eval('('+returndata+')');

//alert(jsonObj.f);
//$("#idCardFront").val(jsonObj.f);
//$("#idCardBack").val(jsonObj.b);

},
error: function (returndata) {
alert(returndata);
}
});