This will smell horrendous but I'm guessing you want HTML in the portal header for good reason ;-)

Upload it as a Static Resource and use JavaScript UserContext.siteUrlPrefix to resolve the path:

<script type="text/javascript">
  document.write(
    "<img " +
      "src='" + UserContext.siteUrlPrefix + "/resource/ns__yourImagePng'" +
    "/>"
  );
</script>

This will smell horrendous but I'm guessing you want HTML in the portal header for good reason ;-)

Upload it as a Static Resource and use JavaScript UserContext.siteUrlPrefix to resolve the path:

<script type="text/javascript">
  document.write(
    "<img " +
      "src='" + UserContext.siteUrlPrefix + "/resource/yourImagePng'" +
    "/>"
  );
</script>

Upload it as a Static Resource and use JavaScript UserContext.siteUrlPrefix to resolve the path:

<script type="text/javascript">
  document.write(
    "<img " +
      "src='" + UserContext.siteUrlPrefix + "/resource/ns__yourImagePng'" +
    "/>"
  );
</script>

Yes, the above smells horrendous and won't be cached. But if you want HTML in a portal header... ;-)

This will smell horrendous but I'm guessing you want HTML in the portal header for good reason ;-)

Upload it as a Static Resource and use JavaScript UserContext.siteUrlPrefix to resolve the path:

<script type="text/javascript">
  document.write(
    "<img " +
      "src='" + UserContext.siteUrlPrefix + "/resource/ns__yourImagePng'" +
    "/>"
  );
</script>