Hello,
We have tested it and the image is added correctly. Maybe you need to set downloadImages as true; we recommend you to read the documentation available on:
https://www.phpdocx.com/documentation/cookbook/insert-images-html
As you are using phpdocx 5.5, the stream mode is not available. This stream mode is only available since phpdocx 7.5 and newer.
Regards.