This feature has been mentioned in https://community.aras.com/b/english/posts/take-hold-of-digital-transformation-with-aras-innovator-12-top-7-questions but I have yet to see an example where someone has achieved this. I tried mimicking how the icon works on the template definition but this still does not work.
{
"content": "image",
"content_binding": "thumbnail",
"col": 0,
"row": 0
},