That image is the one embedded in picture-bind.docx, via:
<w:dataBinding w:xpath="/invoice[1]/items[1]/item[1]/name[1]" w:storeItemID="{3C1B665A-D738-4822-8EFB-14B133235CCB}"/>
You're not successfully altering that binding.
For docx4j / OpenDoPE purposes, I suggest you use the authoring add-in to create your content controls. If that tool detects that you are binding a base64 encoded image, it will create a picture content control automatically.