OLAS/public/PHPWord-0.12.1/samples/Sample_18_Watermark.php

<?php
include_once 'Sample_Header.php';

// New Word document
echo date('H:i:s'), ' Create new PhpWord object', EOL;
$phpWord = new \PhpOffice\PhpWord\PhpWord();

// Begin code

$section = $phpWord->addSection();
$header = $section->addHeader();
$header->addWatermark('resources/_earth.jpg', array('marginTop' => 200, 'marginLeft' => 55));
$section->addText(htmlspecialchars('The header reference to the current section includes a watermark image.'));

// Save file
echo write($phpWord, basename(__FILE__, '.php'), $writers);
if (!CLI) {
    include_once 'Sample_Footer.php';
}