Disney and Marvel revealed four 18 x 24 posters that are available only to fans who purchase the DVD or Blu-ray of the film.
There are three posters by Matthew Ferguson and one by Mark Bagley, based on his Avengers Assemble #1 cover.
The first image below will be available for free to anyone who buys a DVD or Blu-ray and inputs their unique code into the website avengersofferassemble.com.
For an additional $19.99 (plus shipping) you can get the additional three posters.
Free Matthew Ferguson poster
Matthew Ferguson Hulk poster
Matthew Ferguson Iron Man poster
Mark Bagley Avengers poster