why do obituaries of really old people show photos of them when they were in their youth?

Answer 1

Would you want pix of you on your deathbed published?
Think of Mark Twain, for one. We see him in our mind's eye and the noble rascal and irascible genius he was, not as a youth, but as HIM, and that's the way I'd like to be remembered!

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Answer 2

those images are what the deceased would prefer to be remembered as. the younger version, not the older version. besides, we have more photos of us as younger than we have of us as we age.