Part 1:
"What 'thing' have the most people seen with their own eyes ?"
The inside of a human eyelid?
"It has to be something unique ie there is only one of it, it has to be something on this planet (everyones seen the sun) and it has to be something that can be seen completely in one frame of view (lots have seen the Grand Canyon but only parts of it at a time) and multiple views by the same people don't count."
Oh. Um. Freddie Mercury's moustache?
"Part 2:
What image (video or still) have the most people seen ?"
Part 2:
Aeroplanes into the Twin Towers footage. Or Sergio Agueroooooooo scoring for Manchester City against QPR in the 94th minute 13/05/2012. But probably the first.
Thing most seen in real life: The Kaaba?
Image most seen: Hmm. I have previously heard it's the default XP wallpaper, but that's a somehow upsetting answer. Maybe I'll go for Che? But maybe that doesn't count, as it's actually lots of different (very similar) images.