Except it wouldn’t be. They obtained the proper licensing rights to allow them to use all of the characters in that film that belonged to other companies. Technically speaking, it doesn’t matter if you’re a kid in his garage making a “fan-project” or are some big multi-billion dollar production company, as long as you can get the proper licensing permissions from the respective copyright holders, you can legally make whatever you want.
Showing an image is not inherently some form of copyright violation. You could post that image where ever you liked, and short of claiming it as your own or using it to promote something (or some how profit) without permission, there is nothing illegal about it.