> not (data computed from) the entire length of the movie.

I guess we shouldn't publish the running time of movies either.

A checksum is an integer. Stating an integer is fair.

An entire movie can also be represented as an integer.

All information can be represented by integers, or any sequence of symbols, but in this case, a checksum is the equivalent of a name or title -- something only to identify.

> ... something only to identify

Well in this case, the checksum is used "only" to spread illegal copies.

Not sure why else people would want a checksum and store it in a database.

In the same sense that names and titles can also be used to spread illegal copies, but by themselves they are innocuous.

Banning safe behavior to stop bad behavior is negligent policy work. Failure to constrain the effects of policy to its intended target is why people get scared about making videos on repairing Apple products.

It can be identified by it, but you can't reproduce it from the number anymore than you could from the title alone.

Actually, a movie could be represented by a fairly large (infinite even) number of integers that could allow you to fully reproduce or render it. Checksums, however, are merely digital equivalents to titles or other identifiers. They let you know identity, but not content.