问如何在右下角的换行图片中添加图片水印？

EN

private function warpTextImage($text)
{
    $font = $this->font;
    $text_dimensions = imagettfbbox(30, 0, $font, $text);
    $text_width = abs($text_dimensions[4] - $text_dimensions[0]);
    $text_height = abs($text_dimensions[5] - $text_dimensions[1]);
    $img_width = abs($text_dimensions[4] - $text_dimensions[0]) + 40;
    $img_height = abs($text_dimensions[5] - $text_dimensions[1]) + 40;
    $image = imagecreate($img_width, $img_height);
    $background = imagecolorallocate($image, $this->background_color[0], $this->background_color[1], $this->background_color[2]);
    $color = imagecolorallocate($image, $this->text_color[0], $this->text_color[1], $this->text_color[2]);
    $x = ($img_width - $text_width) / 2 - 4;
    $y = ($img_height - $text_height) / 2 + 30;
    imagettftext($image, 30, 0, $x, $y, $color, $font, $text);
    return $image;
}