It is generally considered acceptable to use a photograph as a reference for a painting, as long as the painting is not a direct copy of the photograph. If the painting is a faithful reproduction of the photograph, without any significant changes or additions, it could be considered a copyright violation.
However, if the painting is a transformative work that uses the photograph as a reference but adds significant creative elements, it is less likely to be considered a copyright violation. The key factor is the level of transformation in the painting. If the painting merely copies the photograph, it is likely to be considered a copyright violation. But if the painting adds significant creative elements, such as changes in composition, color, or style, it is less likely to be considered a copyright violation.
It's also worth noting that the photographer's permission is not always required for a painting based on a photograph. If the photograph is in the public domain or has been licensed under a Creative Commons license that allows for derivative works, then the painter may not need to obtain permission from the photographer.
Ultimately, the question of whether a painting based on a photograph is a copyright violation depends on the specific circumstances of the case. It's always best to consult with a legal expert if you have any doubts about the copyright status of a particular work.