D7: Empty image upload field when adding a translation
Figured it out after spending about a whole day of trying in the wrong hook.

Turns out you need the hook_field_widget_form_alter for this.

/**
 * Implements hook_field_widget_form_alter();
 */
function my_module_field_widget_form_alter(&amp;$element, &amp;$form_state, &amp;$context) {
  $field_name = isset($element[0]['#field_name']) ? $element[0]['#field_name'] : NULL;
  if ($field_name === 'field_series_image') {
    if (strpos($form_state['complete form']['#action'], '/edit/add/') &gt; 0) {
      // Works for single image fields (product display).
      $element[0]['#default_value']['fid'] = 0;

      // In case we have more images uploaded, unset all.
      for ($index = $element['#file_upload_delta']; $index &gt; 0; $index--) {
        unset($element[$index]);
      }

      // Also reset the upload delta to 0.
      $element['#file_upload_delta'] = 0;
    }
  }
}


Code above suits our needs.