One way to really simplify what you're looking for is to use the networking library "volley", provided by Google itself. Take a look at the following video, where they discuss several features of the library. https://developers.google.com/events/io/sessions/325304728
The library handles a lot of boilerplate code for you and does all its work asynchronously. You should just be able to fetch the json data, get the original posters url and then set that url as the source of the image. Volley will then automatically and asynchronously load that image.