I think the way you're using them you shouldn't worry about it. From my little understanding, copyright law is very unspecific and muddled but in theory as long as your works are transformative enough they are considered to be 'fair use' of copyrighted material... but to clarify I'm no lawyer haha. I'm a big fan of the painting btw!

Humm... as far as I'm concerned, I personally would not consider the art piece in the first image may have any "copyright" issue to do with the second one. One can easily argue it's copied/referenced the same way as saying it's not. I think you don't need to worry about it this much. And even if you set out to copy a photograph, you will end up with drastically different result. Commercial stuff "reference" other imagery every day. If you are worried, maybe consciously credit the reference you used. Take these two images below as an example, the concept artist does not mention Andrew Wyeth, but it's more than obvious this is certainly a direct reference. (you can see it on artstation /artwork/28xw8B , proko seems to block links)