Most posters are edited (logos and text removed) and thus in some way "fan made", but our preference is at least the stripped down version of official poster over totally fanmade.

// EDIT: I just read in our soon to be contribution bible: "No fanmade posters unless there is no official poster" (as in stripped down version of officials are OK. But creating a poster from scratch is not, unless there is no official poster)

Where is the image from? (Saw your update Marr, so that's what I was getting at with my question.) When I add custom posters I always use a promotional image from the movie, never unrelated images. This one looks very good though and quality is great.

December 2015 fan art by Sysmatic

It's the second piece of fan art posted here: http://www.nolanfans.com/forums/viewtopic.php?f=45&t=16968

Note - currently the only other official poster I've seen is a different aspecting of the soldier's back poster, for a more horizontal format with the tops of the planes cropped out and the background compressed vertically a bit. That has been seen posted in frames in at least two theaters. Here, "ODEON" is not part of the poster.
http://www.nolanfans.com/forums/viewtopic.php?f=45&t=22862&view=unread#p1076416

Is the image related to the movie is what I wanted to ask. The template used for the poster.

My guess is the image uses historical artwork of the actual 1940 event. The movie did not start filming until May 2016.

I don't think anyone knows yet, as it hasn't been released yet. Can't find any stills or so on the website either. http://www.dunkirkmovie.com

// EDIT: There might be a legal issue with fanmade posters by the way. The official posters are of course made to be spread around, but I don't know about fanmade.. Whether it's using actual footage (because copyrights) or totally fan made (because they don't endorse it -- they might not want the film/their names associated with it). I know DeviantArt (artist community) has deleted some "fan art" artworks and such in the past.

@dormouse7 said:

My guess is the image uses historical artwork of the actual 1940 event. The movie did not start filming until May 2016.

Ah yes, in that case it was the correct decision. All good!