Image Uploads are only available on the Teams plan.
Images contained within cells within your Google Sheet will have the following impact on the output:
  • An additional $images object at the root of the JSON document which contains a manifest of all images indexed by filename, containing:
    • url (relative to the URL of the JSON document that was requested)
    • size_bytes
    • mime_type
  • The field containing the image will be output as a JSON object with the keys:
    • $type which will always be set to image
    • filename which is a reference to the key in the root $images object
The filename is a hash of the image contents so if multiple copies of the same image are contained within the source image they will share the same hash/filename and will result in one entry in the $images object. 
{
  "worksheet_name": [
	  {
		  "another_field": "Foo",
		  "name_of_field_containing_image": {
			"$type": "image",
			"filename": "73df8307cc077e05fa9935a4d5a53c53.png"
		  }
	  },
	  {
		  "another_field": "Foo",
		  "name_of_field_containing_image": {
			"$type": "image",
			"filename": "73df8307cc077e05fa9935a4d5a53c53.png"
		  }
	  }
  ],
  "$images": {
    "faf2d6cc94c60397169d406804e0f2cd.png": {
      "url": "/images/faf2d6cc94c60397169d406804e0f2cd.png",
      "size_bytes": 1591,
      "content_type": "image/png"
    },
    "73df8307cc077e05fa9935a4d5a53c53.png": {
      "url": "/images/73df8307cc077e05fa9935a4d5a53c53.png",
      "size_bytes": 1620,
      "content_type": "image/png"
    },
    "69ca799d32aaccbe0b8cbd2cc5d57847.png": {
      "url": "/images/69ca799d32aaccbe0b8cbd2cc5d57847.png",
      "size_bytes": 1625,
      "content_type": "image/png"
    },
    "cb18ad5b0cb7d9f88e1b9e126565df4a.png": {
      "url": "/images/cb18ad5b0cb7d9f88e1b9e126565df4a.png",
      "size_bytes": 1982,
      "content_type": "image/png"
    }
  }
}