But what you found is a photo of a painting ( not the painting in itself of course ! ) .Somebody took a shot of the painting then put it on the net . He is the owner of the copyright . So you must find who took the photo ! In other words , you have the right to use the photo only if you took it yourself  - you went into the museum where the paintings are exposed and took the photo .
I assume you found it as a jpg format - which didn't exist 70 years ago !- how can it be expired?
It's the same problem with music : a song may be in the public domain like Vivaldi , but the interpretation - the orchestra that played it IS NOT !
I guess that if there is a doubt - there's no doubt ! Use it for yourself - not sure that a freebie would be better .

Alice's and GND4's Tailor !
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