Hello,
background images, watermarks and headers/footers can be used to repeat a content in all pages.
If you are creating the DOCX from scratch, you can add the image as a WordFragment when inserting the header or footer. Please check the examples available for the addHeader (http://www.phpdocx.com/api-documentation/layout-and-general/insert-headers-Word-document-with-PHP) method.
If you are using a template, please add a placeholder in the header or footer with the program you are using to generate the templates and then replace the placeholder by an image using the replaceVariableByWordfragment (http://www.phpdocx.com/api-documentation/templates/replace-variable-word-fragment-Word-document) method setting the right target option.
DOCXPath can only be used with the body content.
Regards,
phpdocx support Team