{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/column-formatting.schema.json",
  "elmType": "img",
  "attributes": {
    "src": {
      "operator": "+",
      "operands": [
        "http://covers.openlibrary.org/b/isbn/",
        "@currentField",
        "-S.jpg"
      ]
    }
  }
}