{
  "A_pic": "#image1",
  "B_pic": "#image1",
  "C_pic": "#image2",
  ...
  "~attach": [
    {
      "@id": "image1",
      "data": {
        "base64": "Ugd29ybIHl ...(many bytes omitted)... GQaGVsbG8s="
      }
    },
    {
      "@id": "image2",
      "data": {
        "base64": "GQaGV29yU ...(many bytes omitted)... bIsbG8sgdHl="
      }
    }
  ]
}