url

Either the URL to an image hosted publicly, or a short identifier referencing an image in the Library.

{
    "template": "sample-image",
    "sizes": [
        {
            "width": 1080,
            "height": 1080,
        }
    ],
    "elements": {
        "image1": {
            "url": "https://via.placeholder.com/500/500"
        },
        "image2": {
            "url": "jxnfTsjeWI"
        }        
    }
}