This is actually a very serious shiala!!
when I was in high school, someone mentioned that it may be ossur,
but I didn’t really give it much thought, thinking its prob just a chumra.
well in seminary, I asked my halacha teacher, since many girls were taking pics near/infront/with the sun and he was shocked that
girls in the seminary were doing that since he was convinced we all probably knew that it was assur!
in any case, the next day in class he told the whole seminary that
its forbidden to take pictures of the sun since it falls under catergory of “temuna” ( which ironically is the hebrew word for camera photo) which is part of the prohibition to replicate the
sun and stars in any real form and that its more serious than a drawing whose resemblance to sun may be sujective ( since a photo acurately shows a sun much more than a drawing).
I believed he quoted Harav Moshe Feinstein, but unfort I do not have the actual sources.
After sem, I’v heard it from other people as well that the its a real issur, not just a chumra!