Just take a picture on a device which can't connect to the internet that's secure from virus.

not viable for long term storage

Why would it not be?

Just take a picture on a device which can't connect to the internet that's secure from virus.

not viable for long term storage

Why? the only way someone can access it is locally.

How long do you expect a hard drive to last? 50 years at best, likely much less.

Pen and (acid free) paper lasts hundreds if stored properly.

Smart thinking! How would you store this piece of paper though?

Detailed guide:
http://www.archives.gov/preservation/holdings-maintenance/table-of-contents.html

Shorter articles:
http://www.archives.gov/preservation/family-archives/preserving-family-papers.html
http://jwa.org/stories/how-to/preservation

The gist is that you should store in an appropriate enclosure, in average room temperature and humidity, away from light. You should definitely read the above links if you're interested, since there's obviously more to it.

Thanks for the links I'll have a look tommorrow as its late here sounds like a good way to store it for long term.