Topic on Extension talk:PortableInfobox

According to the FANDOM documentation, the <image> tag is allowed under <group>, but when I try to use it in an infobox, images simply don't display. This is the code I'm using:

  <group layout="horizontal">
    <image source="flag">
      <caption source="flag_caption">
        <default>Flag</default>
      </caption>
    </image>
    <image source="coat_of_arms">
      <caption source="coat_of_arms_caption">
        <default>Coat of arms</default>
      </caption>
    </image>
  </group>

Is there any other way to fix it or it's just not possible?