gistfile1.txt

{
    "application_id": "YOUR_APP_ID",
    "src": "https://s3.amazonaws.com/img.blitline/sky.jpg",
    "pre_process": [
        {
            "job": {
                "src": "https://s3.amazonaws.com/img.blitline/samples/city.png",
                "functions": [
                    {
                        "name": "composite",
                        "params": {
                            "src": "https://s3.amazonaws.com/img.blitline/samples/circle_crop_mask.png",
                            "composite_op": "CopyOpacityCompositeOp",
                            "as_mask": true,
                            "scale_to_match": true
                        },
                        "save": {
                            "image_identifier": "MY_COMPOSITED_IMAGE"
                        }
                    }
                ]
            }
        }
    ],
    "functions": [
        {
            "name": "composite",
            "params": {
                "gravity": "CenterGravity",
                "src": "&MY_COMPOSITED_IMAGE"
            },
            "save": {
                "image_identifier": "Output of city cropped, composited onto sky"
            }
        }
    ]
}