Transformer for Images

// if form is mapped => false;      
$img = $form->get('img')->getData();

//if form is mapped => true
$img = $user->getImg();
      
if ($img !== NULL) {
 // Generate a unique name for the file before saving it
 $fileName = md5(uniqid()) . '.' . $img->getExtension();

 // Move the file to the directory where brochures are stored
 $img->move(
   $this->getParameter('user_images'),
   $fileName
 );

 // Update the 'img' property to store the img file name
 // instead of its contents
 $user->setImg($fileName);
}