[smaudet]

Hmm I don't think they are cryptographically protected, it's a security by difficulty thing (obscurity?) - iso is not a "simple" format so corrupting is not simple, either.

On the other hand as you said, physical media can have a strong(er) security guarantee (write once at the physical layer), and iso's are easier to burn than disk images...

Optical media can still be bought and drives still work fine...and there are other advantages to optical media (such as longevity) that as of yet drives can't replicate.

[eptcyka]

The bytes can still be overwritten, you dont need to change the structure of the image's filesystem to do that.