Hello,
UPDATE: Remove an image that contains a placeholder
We recommend you to use the method removeWordContent from DOCXPATH:
http://www.phpdocx.com/documentation/introduction/docxpath
http://www.phpdocx.com/api-documentation/docx-path/remove-elements-in-docx
Besides this page docs, please check the included examples in the package.
This method allows to remove any Word content, so it allows to do exactly what you need.
Regards.