thumbnail

Allows you to use thumbnail in the embed. You can set only url of the thumbnail. There is no way to set width/height of the picture.

Example:

{
  "embeds": [{
    "thumbnail": {
      "url": "https://upload.wikimedia.org/wikipedia/commons/3/38/4-Nature-Wallpapers-2014-1_ukaavUI.jpg"
    }
  }]
}

thumbnail example