What’s with the zigzagging stripes on the road?
Here’s one that may be more widespread than Iwo Jima, if not Abbey Road:
But if you look at the examples, many are not U.S.
The Wright Bros. first flight is often claimed to hold that distinction.
It’s to get drivers to slow down.
I agree; I think that the OP’s question is heavily US-centric.
If you show that photo to people outside the US, I doubt that it would be widely recognized.
Why would the Chinese, the Indians, or other heavily populated countries make lots of copies of this photo? They have their own iconic images to spread around, like Mao or Ghandhi.
Just as a personal anecdote, I would say I’ve seen more of the Che and Mao pictures than the Iwo Jima picture in popular culture; I’ve never seen it on a t-shirt for instance, but have seen lots of Mao and Che t-shirts and posters.
You’re not allowed to park in those areas.
But again, look at the examples. Many countries have used the image with no U.S. context. The photo was even the basis for the image on Sri Lankan currency. http://www.usni.org/iwo-jima-parody-photos
Thanks 
My explanation is the correct one 
Some of my fellow canadian dopers may remember a cartoonist from the Toronto Sun, one Andy Donato.
Shortly after the Iranians taking the embassy, he had that iconic image drawn, so that it was being planted in the Ayatollahs Ass.
Declan
Google hits for “flag raising” “Iwo Jima”: 194,000
Google hits for “Abbey Road” “cover”: 20,800,000
O.K., it’s not really an accurate way to test this, but what is? Find me any evidence that the Iwo Jima picture is parodied more than the Abbey Road one.
Are there really a lot of tributes, parodies, etc. of that Capa photo?
As for the general question of “most viewed photo of all time,” it looks like my guess is certainly in the running.
That would be my bet.
I used to get the 139 bus down Abbey Road every day and I don’t think there has ever been a single journey in which the bus didn’t have to stop whilst people did their own version of that picture. All day long, every day, for decades, people have been recreating that photo.
I remember a similar poster from when I was a kid - it was the US Olympic Hockey team planting a giant hockey stick with the flag in the Ayatollah’s ass. Very 1980.
I would think the most reproduced photo would be the standard headshot of Joseph Stalin. That was hung on the wall in every government office in the entire Soviet Union (which was a lot bigger back then) and even appeared on the wall of a great many family homes. That has to be a huge number of copies of his photo.
Heck, Barack Obama’s photo hangs in 32,000 US Post offices (plus probably other government offices) – that’s a lot of copies right there.
Photos of the king and sometimes the queen hang in just about every Thai household (but not ours), and the population is 70 million. Not to mention offices, both government and private. Granted, they are not all the exact same photo, but there is a limited number of types. I’ve also seen this in Indonesia during Suharto and various other countries with strongman rulers.
I have never seen that picture before in my entire life.