Bounding Box

Each of the boxes is specified with an object containing left, top, width, and height keys, and optional label.

{
    "lines": [
        ...
    ],
    "polygons": [
        ...
    ],
    "boxes": [
        {
            "label": "car",
            "height": 97,
            "width": 147,
            "top": 229,
            "left": 300
        }
    ],
    "cuboids": [
        ...
    ]
}