Well, a quite challenging painting! I think this is the reference picture You worried about for copyright.
Frankly it looks like a quite standard picture recording a most common image of a horse running on a beach. I don't see any particular creativity or originality which could lead anyone taking this picture to claim any whatsoever copyright. I made many most interesting shots of clouds and skys and I can hardly imagine I might copyright cloudy skies for this. We're getting crazy about copyrights and patents and try to make money out of any real merit we may have. Anyway there's no worldwide law and jurisdiction ... fortunately, and we should absolutely legally avoid that huge global players are entitled book for themeselves even the air we breathe or the words our ancestorse invented in each language which they didn't create!
Personally I just immediatly see these possible interpretation problems to my sight:
the horse is too black and almost anywhere. Usually very few points have the absolutely darkest tone and here we're not even in a case of low-key image;
the head and the neck seems too massive to me, quite heavy;
the black spot just over the horse's left eye seem an eye itself in the wrong place. It's so dark and predominant that You cannot immediately recognize what the true eye is.
Panta rei (everything flows)!