When is a masterpiece not a masterpiece?

At first glance, and for a brief moment, I imagined myself the finder of a lost painting by a Dutch Master and that endless rummaging through boxes of framed pictures in charity shops might have paid off!  No not really, that was never the point although….

On closer inspection I decided that this was a copy but I cannot find anything similar when I search for it on the internet.  Here it is:

It certainly isn’t a Monet (Windmill at Zaandam):

Or a Boudin (Windmills and Canal neat Dordrecht 1884):

And there are many, many hundreds more but nothing quite like mine.  Any suggestions?

Just out of interest, the most expensive paintings sold have been for $300 million and are Willem de Kooning’s Interchange and Paul Gaugin’s When will you Marry?