{
    "$schema": "http://adaptivecards.io/schemas/adaptive-card.json",
    "type": "AdaptiveCard",
    "version": "1.1",
    "height": "stretch",
    "body": [
        {
            "type": "Container",
            "height": "stretch",
            "backgroundImage": {
                "url": "${placeholder}",
                "fillMode": "Cover",
                "horizontalAlignment": "Center",
                "verticalAlignment": "Center"
            }
        }
    ]
}