I would be extremely surprised if any civil court found Churchill innocent of copyright infringement.

My guess is that he will argue that he took an original work and "interpreted" it. It's been done a million times, but either with permission, without permission as a satire (which is allowed and which this obviously is not), or without permission on a masterwork in the public domain, which still must be cited somehow.

Churchill has made some changes. The image reversal, the change in the background color... Nevertheless, he has taken the essence and heart of the work and claimed it as his own original. Not allowed.

A while back, George Harrison had a run-in with Motown over the tune of "My Sweet Lord", parts of which very closely resembles "He's So Fine". Coincidental reproduction of sound patterns can happen, because there are only a limited number of notes in the scale. Nevertheless, Harrison lost. He was not found to have maliciously infringed copyright, but unconscious or not, he did reproduce enough of the original tune to be found culpable.

Unlike that case, Churchill could not possibly have unconsciously reproduced a pattern from memory. This picture is so detailed that no one can miss the fact that it's been stolen.

I hope Thomas Mails's kid sues Churchill's socks off for this.