将Ajax POST表单转换为PHP

Trying to post my form using Ajax. Using Apache Cordova but can't seem to send it to my php form. Any ideas of how to get my form to work would be appreciated.

  <script type="text/javascript">    
$('#userform').submit(function(){
    var postData = $(this).serialize();

    $.ajax({
        type: 'POST',
        data: postData,
        url: 'http://myurl/dbInsertUserslocal.php',
        success: function(data){
            console.log(data);
            alert('User successfully added');
        },
        error: function(){
            console.log(data);
            alert('There was an error adding New User');
        }
    });
    return false;
});
</script>

and my form looks like:

      <form id="userform" method="Post">
      <div class="row">
    <div class="large-4 columns">
      <label>First/Last Name
        <input type="text" name="firstlast" />
      </label>
    </div>
      </div>
    <div class="row">
    <div class="large-2 columns">
      <label>Title
        <select name="title" >
          <option value=""></option>
          <option value="Inspector">Inspector</option>
          <option value="Tech">Technician</option>
          <option value="Supervisor">Supervisor</option>
        </select>
      </label>
  </div>
  </div>

    <div class="row" >
        <div class="large-12 columns">  
           <hr class="intro-divider">
                <input type="file" capture="camera" accept="image/*" 
                     id="snap" name="photo">
                      </div>
                           </div>
               <hr class="intro-divider">   
           </div>
         </div>
       <div class="row">
    <div class="large-2 columns">
        <button class="tiny" type="submit" value="Submit" 
             id="submit" data-role="button" data-ajax="false">Add User</button>
    </div>
     </div>
    </form> 

If you include the file in form, you must use multipart/form-data.

<form id="userform" method="Post" enctype="multipart/form-data">

serialize method can't see the file data. By using the FormData object instead of serialize method, the javascripts code becomes

$(function(){
$('#userform').submit(function(){
    var fd = new FormData( $(this)[0] );
    $.ajax({
        type: 'POST',
        processData: false,
        contentType: false,
        data: fd,
        dataType: "text",
        url: 'http://myurl/dbInsertUserslocal.php',
        success: function(data){
            alert( data );
            alert('User successfully added');
        },
        error: function(){
            alert('There was an error adding New User');
        }
    });
    return false;
});
});

However, some devices does not equip the FormData object. Check http://caniuse.com/#search=FormData