"Some could be.." is computing by coincidence, and I'm not a fan of that logic. You can refer to the 2007, 2009, and 2012 studies for measured data on server farms.
How do you know? Just the other day I pushed a TS video stream through the script that accidentally modified some bytes (I didn't even bother to analyze the exact changes). There were occasional artifacts observable, but the stream played nevertheless. Which is how the players are being made: to be able to resynchronize even on bigger errors. Somebody who programs these things can surely tell you much more about that.
I was able to notice that because I played the stream in mplayer while watching the console output. So I saw the "debug messages" detecting "something" wrong, and stopped seeing them once I've corrected the script. It was the messages, not the "watching" that made me sure.
Well... I can imagine there are enough people who won't care too.
Note that the chance for corruptions increases as long as the data remain in RAM unsaved and only much later get to be saved. We are lucky that, at least in private use, we typically copy the data to the medium without keeping it too long only in the RAM (order of seconds or less). So that also reduces the chances of our pictures being saved with the wrong bits.
Though, I usually only notice it years after the fact. I have a lot of photos and a lot of videos and only view a few old ones on occasion.
> "Some could be.." is computing by coincidence
That second paragraph of mine is mostly superfluous, and you seem to have read more into it than I intended. Whoops. I should have been more clear. I was not trying to make any sort of claim as to how to do computing. I was only trying to show that there are other possibilities that you would need to investigate and reject before going from your premises to that particular conclusion.
Also, I don't think images stay for too long in RAM. Your HDD definitively has ECC.
Was fun finding a bunch of my own photos like that. Luckily that was on a disposable copy and not primary storage, but it was enough to put me completely off non-checksumming filesystems.