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.