I have a table of student data and a folder with their images. I want to replace some imges but it is not working. please help. I got this code somewhere and changed it according to my need but it is not working. code is in two parts. The first part is a form with a jquery action part in PHP. please help what is wrong with this code
    <h1 class="page-head-line">Student Photo Change</h1>
<div class="container" style="width:900px;">  
   </div>
  </div>  
 </body>  
</html>
<div id="imageModal" class="modal fade" role="dialog">
 <div class="modal-dialog">
  <div class="modal-content">
   <div class="modal-header">
    <button type="button" class="close" data-dismiss="modal">×</button>
    <h4 class="modal-title">Add Image</h4>
   </div>
   <div class="modal-body">
    <form id="image_form" method="post" enctype="multipart/form-data">
     <p><label>Select Image</label>
     <input type="file" name="image" id="image" /></p><br />
     <input type="hidden" name="action" id="action" value="insert" />
     <input type="hidden" name="image_id" id="image_id" />
     <input type="submit" name="insert" id="insert" value="Insert" class="btn btn-info" />
      
    </form>
   </div>
   <div class="modal-footer">
    <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
   </div>
  </div>
 </div>
</div>
 
<script>  
$(document).ready(function(){
 
 fetch_data();
 function fetch_data()
 {
  var action = "fetch";
  $.ajax({
   url:"photochangeaction.php",
   method:"POST",
   data:{action:action},
   success:function(data)
   {
    $('#image_data').html(data);
   }
  })
 }
 $('#add').click(function(){
  $('#imageModal').modal('show');
  $('#image_form')[0].reset();
  $('.modal-title').text("Add Image");
  $('#image_id').val('');
  $('#action').val('insert');
  $('#insert').val("Insert");
 });
 $('#image_form').submit(function(event){
  event.preventDefault();
  var image_name = $('#image').val();
  if(image_name == '')
  {
   alert("Please Select Image");
   return false;
  }
  else
  {
   var extension = $('#image').val().split('.').pop().toLowerCase();
   if(jQuery.inArray(extension, ['gif','png','jpg','jpeg']) == -1)
   {
    alert("Invalid Image File");
    $('#image').val('');
    return false;
   }
   else
   {
    $.ajax({
     url:"photochangephotochangeaction.php",
     method:"POST",
     data:new FormData(this),
     contentType:false,
     processData:false,
     success:function(data)
     {
      alert(data);
      fetch_data();
      $('#image_form')[0].reset();
      $('#imageModal').modal('hide');
     }
    });
   }
  }
 });
 $(document).on('click', '.update', function(){
  $('#image_id').val($(this).attr("id"));
  $('#action').val("update");
  $('.modal-title').text("Update Image");
  $('#insert').val("Update");
  $('#imageModal').modal("show");
 });
 $(document).on('click', '.delete', function(){
  var image_id = $(this).attr("id");
  var action = "delete";
  if(confirm("Are you sure you want to remove this image from database?"))
  {
   $.ajax({
    url:"photochangephotochangeaction.php",
    method:"POST",
    data:{image_id:image_id, action:action},
    success:function(data)
    {
     alert(data);
     fetch_data();
    }
   })
  }
  else
  {
   return false;
  }
 });
});  
</script>
code of photochangeaction.php
<?php
if(isset($_POST["action"]))
{
 
 if($_POST["action"] == "fetch")
 {
  $query = "SELECT id, form_no, sname, photo FROM student  where center_code='1001'";
  $result = mysqli_query($conn, $query);
  $output = '
   <table class="table table-bordered table-striped">  
    <tr>
     <th width="10%">ID</th>
     <th width="70%">Image</th>
     <th width="70%">File Name</th>
     <th width="70%">Student Name</th>
     <th width="10%">Change</th>
     
    </tr>
  ';
  while($row = mysqli_fetch_array($result))
  {
     
   $output .= '
    <tr>
     <td>'.$row["id"].'</td>
     <td>
      <img src="'.($row['photo'] ).'" height="60" width="75" class="img-thumbnail" />
     </td>
     <td>
      '.($row['photo'] ).'
     </td>
     <td>
      '.($row['sname'] ).'
     </td>
     <td><button type="button" name="update" class="btn btn-warning bt-xs update" id="'.$row["id"].'">Change</button></td>
   
    </tr>
   ';
  }
  $output .= '</table>';
  echo $output;
 }
 
 if($_POST["action"] == "update")
 {
  $file = $_FILES["image"]["tmp_name"];
 // $image=PATHINFO($_FILES['image']['name']);
  $form_no=$conn->query('select form_no from student WHERE id = '.$_POST["image_id"].'');
  $newFilename=$form_no . '.' . $file['extension'];
    if (file_exists("sphoto/" . $newfilename))
        {
        // file already exists error
            unlink("sphoto/$newfilename");
            move_uploaded_file($_FILES["image"]["tmp_name"], "sphoto/" . $newfilename);
            $photo='../sphoto/' . $newFilename;
            $query = "UPDATE student SET photo = '$photo' WHERE id = '".$_POST["image_id"]."'";
                if(mysqli_query($conn, $query))
                    {
                        echo 'Image Updated into Database';
                        echo "File Overwritten";
                    }
            
        }
        else
        {       
            move_uploaded_file($_FILES["image"]["tmp_name"], "sphoto/" . $newfilename);
            echo "File uploaded successfully."; 
            $query = "UPDATE student SET photo = '$photo' WHERE id = '".$_POST["image_id"]."'";
                if(mysqli_query($conn, $query))
                    {
                        echo 'Image Updated into Database';
                        echo "File Overwritten";
                    }
        }
 }
}
?>

 
    