The two J-20s are not just duplicated. Look at how differently the left canard and right vertical stabilizer intersect for each aircraft. There're other noticeable differences too, like the shadows on the right ventral fins.
It could be a matter of one pilot pushing the door close button slightly later than the other?
Agreed and even this image has probably been modified by some sort in order to look much better - HEY, it is an advertising poster for a film! - I cannot understand how anyone does not notice the difference. They are too much different both in position and flight situation !
YES, we've seen a lot more or less obviously psed images but here to think it is a CGI is a bit farfetched.
Deino