Welcome to Indietalk, enjoy your stay.
It's okay to bark up the pipe dream tree. Those who don't or won't shouldn't be in this part of the forrest.
My theory is, anybody can dream it. Making it work seperates the men from the boys.
The reflection part I understand but what do you mean by "considerations" to adheare to? Are you worried the owner of the painting is going to get mad and sue you for copyright infringement? Or are you worried about making the shot work?
If it's the former, I have no idea. I would think if you purchased your own 'copy' of the painting (ie in poster form) then it's yours and you can do what you like with it. If it's in a book and you copy it, or find it on the Internet and copy it to your hard drive, well now we need a lawyer.
To pull the shot off I'm thinking green screen the painting/picture or use a vector graphic and super impose it on your shot of the sun glasses. Since the picture won't move you don't have to map the head movements of your actor.
I think if you shoot the actor with shades looking into a mirror you can turn the mirror so you don't get the camera in the way then have the actor turn his head to give the illusion that the camera is right in front of his face. Then just flip the shot in post.