tCMS/www/templates/html/components/preview.json

{
   "x-tcms-include" : {
      "name" : "preview",
      "description" : "The preview image: the upload itself, and the href it turned into on the last save."
   },
   "type" : "object",
   "properties" : {
      "preview" : {
         "type" : "string",
         "x-tcms-label" : "Preview Image"
      },
      "preview_file" : {
         "type" : "upload",
         "x-tcms-label" : "Preview Image",
         "x-tcms-input" : "file"
      }
   }
}