function public_news_image_validation( $valid_obj ) {
  if ( empty( $_FILES ) ) return $valid_obj;
  $form_id = $valid_obj['form']['id'];
  $formFields = &$valid_obj['form']['fields'];
  $page_number = GFFormDisplay::get_source_page( $form_id );
  foreach ( $formFields as &$field ) {
  if ( $page_number > 0 && $field["pageNumber"] != $page_number ) continue; //paged form scenario - only validate fields that are on current page
    if ( in_array(
        ( $field_type = RGFormsModel::get_input_type($field) ),
        array( 'fileupload', 'post_image' )
      )
    ) {

      $field_id = $field['id'];
      $input_name = 'input_' . $field_id;

      if ( $field['failed_validation'] ) return $valid_obj;
      $file_info = RGFormsModel::get_temp_filename( $form_id, $input_name );
      $temp_filepath = RGFormsModel::get_upload_path($form_id) . "/tmp/" . $file_info["temp_filename"];

      if ( file_exists( $temp_filepath ) ) {
        $bytes = filesize( $temp_filepath );
        $dims = @getimagesize( $temp_filepath );
      }
      elseif ( isset( $_FILES[$input_name] ) && !empty( $_FILES[$input_name] ) )  {
        $bytes = $_FILES[$input_name]['size'];
        $randname=mt_rand() . $_FILES[$input_name]['name'];
        $_FILES[$input_name]['name']=$randname;
        $dims = @getimagesize( $_FILES[$input_name]['tmp_name'] );
      }
      else return $valid_obj;
      $max_size = 1024*4000; // 4000kb
      if ( $bytes > $max_size ) {

        unset( RGFormsModel::$uploaded_files[$form_id][$input_name] );
        unset( $_FILES[$input_name] );
        $field['failed_validation'] = true;
        $field['validation_message'] = sprintf( __( 'File upload size (%s) exceeded', 'gravityforms' ), $max_size/1024 . 'kb' );
        $valid_obj['is_valid'] = false;
        return $valid_obj;
      }
      if ( ! empty( $dims ) && is_array( $dims ) ) {
        list( $up_width, $up_height ) = $dims;
        if ( min( $up_width, $up_height ) < 300 ) { //smallest image size should be at least 300px

          unset( RGFormsModel::$uploaded_files[$form_id][$input_name] );
          unset( $_FILES[$input_name] );
          $field['failed_validation'] = true;
          $field['validation_message'] = sprintf( __( 'Image should be at least %s', 'gravityforms' ), '300x300 (px)' );
          $valid_obj['is_valid'] = false;
          //return $valid_obj;
        }
      }
    }
  }
  return $valid_obj;
}

add_action( 'gform_validation', 'public_news_image_validation' );