Perhaps in his Pirush Mishnayos on Avoda Zara he says that. I sort of remember it being there.
Tosafos points out that this Mitzva is unique in that we are allowed to commission a non-Jew to do it for us. That being the case, since it’s not like creating an Avoda Zara, the problem might be with the act of drawing it. If that is the case, then a photograph wouldn’t be a problem. The fact is that nobody checks to make sure the sun or moon is not in the background before taking a picture.