{
    "books": [
    {
      "id": 2331,
      "image": "http://lol.org/flower.png",
      "images": [
                 {
                  "256x144": "http://lol.org/bee.png",
                  "650x320": "http://lol.org/fly.png"
                  }
                 ],

....

$data = json_decode($jsondata,true);
$gg = sizeof($data['books']);
for($x=0;$x<$gg;$x++){

$image = $data['books'][$x]['image'];

$image = ($data->{'books'}->{'images'}->{'320x180'});

  $image = $data['books']['images'][$x]['320x180'];

$image = $data['books'][$insertIndexHere]['images'][$insertIndexHere]['320x180'];