For an obituary for Leonardo I'd use a portrait of Leonardo.
I'll add a bit more nuance to that - people don't always read every word of a newspaper article. That's fine, it's why the inverted pyramid [0] model is used. If there's a big headline (Neil Armstrong Dies) and a single photo (the one of Buzz Aldrin) and the fact it's not a photo of Armstrong is in a little caption, it's going to contribute to the misconception that the photo of Aldrin is actually a photo of Armstrong.
Contributing to misconceptions is bad and should be avoided. Luckily this is easy - just use the photo of Armstrong in the lunar lander.
On the other hand, it's unlikely anyone would mistake Leonardo and the woman in the Mona Lisa so it wouldn't seem so bad to me!
I confess that I'm puzzled by what seems to be an assumption that there's only going to be a single photo used in an obituary of one of the world's most historic figures. I agree that if I can only have a single photo in an obit, it should be a picture of the subject of the obit! I also think using a picture where one cannot see the subject's face would be tacky, regardless of who is behind the visor.
I might have some bias here as someone who reads primarily online media, but I haven't observed most venues limiting themselves to a single photo.
Different news websites and publications have different styles - Sites like [0-5] seem to have decided on having one leading photo, with optional click-through galleries. On the other hand [6-8] have multiple images. Perhaps the websites of print publications have a tradition of more-text-fewer-pictures.
Interestingly, the BBC's obit had multiple videos (represented by a picture with an icon over it, as is the convention) but no still photos. I am obviously not an expert on this :) but I thought their article looked great.