Not sure how to complete these Json Decoder example.

Decoder.elm

type alias Answer =
    { name : String,
      imgUrl : String
    }

decodeAnswers : Json.Decoder (List Answer)
decodeAnswers =
  let
    imageUrlDecoder = ("url" := Json.string)
    imagesDecoder = Json.list imageUrlDecoder --Decoder List String
    firstImageDecoder = ??
    albumDecoder = Json.object2 Answer ("name" := Json.string) firstImageDecoder
  in
    (Json.at ["albums", "items"] (Json.list albumDecoder))

example.json

{
  "albums" : {
    "href" : "https://api.spotify.com/v1/search?query=foo&offset=0&limit=20&type=album",
    "items" : [ {
      "album_type" : "compilation",
      "available_markets" : [ "AD", "AR", "AT", "AU", "BE", "BG", "BO", "BR", "CA", "CH", "CL", "CO", "CR", "CY", "CZ", "DE", "DK", "DO", "EC", "EE", "ES", "FI", "FR", "GB", "GR", "GT", "HK", "HN", "HU", "IE", "IS", "IT", "LI", "LT", "LU", "LV", "MC", "MT", "MX", "MY", "NI", "NL", "NO", "NZ", "PA", "PE", "PH", "PL", "PT", "PY", "RO", "SE", "SG", "SI", "SK", "SV", "TR", "TW", "US", "UY" ],
      "external_urls" : {
        "spotify" : "https://open.spotify.com/album/1zCNrbPpz5OLSr6mSpPdKm"
      },
      "href" : "https://api.spotify.com/v1/albums/1zCNrbPpz5OLSr6mSpPdKm",
      "id" : "1zCNrbPpz5OLSr6mSpPdKm",
      "images" : [ {
        "height" : 640,
        "url" : "https://i.scdn.co/image/d181666ebeda1aa062a5f0250b85be6150badd0f",
        "width" : 640
      }, {
        "height" : 300,
        "url" : "https://i.scdn.co/image/9ed1dc82d30f1b519a97659f401c2397cfd68878",
        "width" : 300
      }, {
        "height" : 64,
        "url" : "https://i.scdn.co/image/e08a4a69c8c83ecf2437f15ba706db3f35106a6b",
        "width" : 64
      } ],
      "name" : "Greatest Hits",
      "type" : "album",
      "uri" : "spotify:album:1zCNrbPpz5OLSr6mSpPdKm"
    }, {
      "album_type" : "album",
      "available_markets" : [ "AD", "AR", "AT", "AU", "BE", "BG", "BO", "BR", "CA", "CH", "CL", "CO", "CR", "CY", "CZ", "DE", "DK", "DO", "EC", "EE", "ES", "FI", "FR", "GB", "GR", "GT", "HK", "HN", "HU", "IE", "IS", "IT", "LI", "LT", "LU", "LV", "MC", "MT", "MX", "MY", "NI", "NL", "NO", "NZ", "PA", "PE", "PH", "PL", "PT", "PY", "RO", "SE", "SG", "SI", "SK", "SV", "TR", "TW", "US", "UY" ],
      "external_urls" : {
        "spotify" : "https://open.spotify.com/album/2qwN15acAl3sm3Idce5vK9"
      },
      "href" : "https://api.spotify.com/v1/albums/2qwN15acAl3sm3Idce5vK9",
      "id" : "2qwN15acAl3sm3Idce5vK9",
      "images" : [ {
        "height" : 640,
        "url" : "https://i.scdn.co/image/6366b355d9f5abe6a4b74c26486cec8877960b8a",
        "width" : 640
      }, {
        "height" : 300,
        "url" : "https://i.scdn.co/image/7cef7ca470cd0b2e07924f28f4eed8af65ad7a89",
        "width" : 300
      }, {
        "height" : 64,
        "url" : "https://i.scdn.co/image/4614809bd85219e78fdb5dd0d884cddef7f29f82",
        "width" : 64
      } ],
      "name" : "Sonic Highways",
      "type" : "album",
      "uri" : "spotify:album:2qwN15acAl3sm3Idce5vK9"
    }],
    "limit" : 20,
    "next" : "https://api.spotify.com/v1/search?query=foo&offset=20&limit=20&type=album",
    "offset" : 0,
    "previous" : null,
    "total" : 330
  }
}