The application images are treated like any other image by the API. You can find them by querying the list of images. For instance, here’s the result for the Docker image:

    {
      "id":6375976,
      "name":"Docker 1.2.0 on Ubuntu 14.04",
      "distribution":"Ubuntu",
      "slug":"docker",
      "public":true,
      "regions":[
        "nyc1",
        "ams1",
        "sfo1",
        "nyc2",
        "ams2",
        "sgp1",
        "lon1",
        "nyc3",
        "ams3"
      ],
      "created_at":"2014-09-26T19:48:01Z"
    }

Note, the docker slug. You can use this in place of the image ID when creating a droplet as it is guaranteed to be stable while the ID may change if the image is updated.

Remember that API results are paginated. Sometimes this trips people up as they don’t realize the image they are looking for is on the next page.