ExportWebMap

{
    "operationalLayers": [
        {
            "id": "layer1",
            "url": "http://<servername>:6080/arcgis/rest/services/Demo/Japan/MapServer",
            "opacity": 1,
            "visibility": true,
            "visibleLayers": [
                                    0
            ]
        }
    ],
    "mapOptions": {
        "extent": {
            "xmin": 136,
            "ymin": 35,
            "xmax": 137,
            "ymax": 36,
            "spatialReference": {
                "wkid": 4326
            }
        }
    },
    "exportOptions": {
        "dpi": 96,
        "outputSize": [200,100]
    }
}