How to upload a file in a block configure form

gistfile1.php

function hook_block_configure($delta = '') {
  $form['image'] = array(
    '#title' => t('Image'),
    '#type' => 'managed_file',
    '#description' => t('The uploaded image will be displayed on this page using the image style choosen below.'),
    '#upload_location' => 'public://header_blocks/',
  );

}

function hook_block_save($delta, $edit) {
  foreach($edit as $key => $updated_content ) {
    if($key == 'image') {
      if(isset($edit[$key]) && is_numeric($edit[$key]) && $edit[$key] > 0) {
        $file = file_load($edit[$key]);
        $file->status = FILE_STATUS_PERMANENT;
        file_save($file);
        file_usage_add($file, 'header_blocks', 'node', $nid);        
      }
    } 
  }
}

$key = 'image';
if(isset($edit[$key]) && is_numeric($edit[$key]) && $edit[$key] > 0) {
$file = file_load($edit[$key]);
$file->status = FILE_STATUS_PERMANENT;
file_save($file);
file_usage_add($file, 'header_blocks', 'node', $nid);
}