json_schema: {
      "$schema": "http://json-schema.org/draft-04/schema#",
      "title": "Image schema",
      "description": "Description of an image that is available for presentation of a step",
      "image": {
          "type": "object",
          "description": "data about a image",
          "properties": {
              "filename": {
                  "type": "string",
                  "description": "Filename of image in local filesystem"
              },
              "alt": {
                  "type": "string",
                  "description": "Alternative text for image"
              }
          },
          "required": [
              "filename"
          ],
          "additionalProperties": false
      },
      "properties": {
          "image": {
              "$ref": "#/image"
          }
      },
      "required": [
          "image"
      ]
  }