Hi Alessandra,
thanks for your interesting feedback and info.
At the time of getting the right to publish the work (and yes, the word exclusive does appear on the contract) the artist's son had no interest in it and basically said I could do what I wanted with it.
It's an interesting story. The picture was on a calendar given to me by an Indian woman back around 1972, which I kept for years as I liked it so much. I have never seen it anywhere else in India, and when I decided ot use it for a book, I had a hell of time tracking down the artist -- luckily, his signature was on the picture so I knew his name. My search took me to various collectors of Indian calendar art and one researcher happened to have interviewed the artist many years ago, and even had records of the address. It was in a remote town in Tamil Nadu. It so happened that my son was in Tamil Nadu at the time -- and India is HUGE so that was a stroke of luck! -- so I sent him in a taxi to hunt down the address. I didn't know if anyone lived there, and doubted that the artist was alive.
It was a day's journey, and he had to take an interpreter, but it was successful.
The son lived in the house and was a jeweller. He had no interest in his father's art or in profiting form it. I am probably the only person in India, and the world, interested in keeping it alive! He was very surprised that my son turned up out of the blue and he signed for me, but really, even that he thought superfluous.
You must understand that Indians do see things differently from Westerners and I am sure I am doing no wrong ethically be letting another use it. Especially where religious stuff is concerned -- and this is religious art -- they believe it belongs to the world and that no-one can "own" it. Plus, oral permission is just as good as written, and I have the oral.
However, I will change the wording as that was what I was mostly worried about -- did I or the artist (heirs) hold the copyright. So thank you!