[jrochkind1]

What determines whether a hash is "cryptographic"? What would make it suitable for change-detection but not be "cryptographic"? Is the claim here that it would not be suitable for detecting "malicious" changes, but is still suitable for detecting "natural" changes?

[gleenn]

A couple features are that is hard for an attacker to find a collision, and it is hard to reverse the original data from the hash. Both can cause serious security problems but aren't necessary in something like this where most image changes are "natural" and you gain speed by weakening those constraints.