First do not add code in body block. Create a custom module.

To add image field please refer Drupal Form API.

Eg.

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