I write these words in steel, for anything not set in metal cannot be trusted.

Thin concrete slabs are extremely brittle.

Don’t forget, you also need drives that work that long and connect to computers or some other device to utilize the bits, and the bus they use must be available and working, and the disk format they’re written in must be readable, and the images themselves encoded with an algorithm that we still have access to, etc. it’s not just the media.

I think it’s possible, thanks to the retro enthusiasts, we still have access to some things from the 70s and 80s, but they’re getting fewer and fewer, especially in a working state. That’s only 50yrs ago. What happens when you want to go 100? Or 500? A few thousand? We are familiar with journals from the Civil War, and have found items and notes from Egypt, Roman, and Ancient Greek civilizations, how can we preserve what happened in the currently information rich time we live in, for future generations? Especially as much of it migrates online to blog posts and social networks and news sites that eventually shut down due to corporate issues or shifting internet traffic?

Is it? It's rather expensive and would you really know, if the data is gone or corrupted?

You'd have to download every single file in certain intervals and check it. That's not really low complexity.

You have to hope neither goes out of business either.