If someone finds a lost iPhone, would it be useless if the original owner had the phone turned off?

If someone finds a lost iPhone, would it be useless if the original owner had the phone turned off? - 1

No one has the codes to get past the settings. And if you did have the code and turn the phone on, it would notify apple and the cops.

You don't want to get caught, do you?

If the original owner contacts the carrier, the carrier blacklists that phone's ESN or IMEI, and that make the phone useless to anyone else, as far as ever using that phone on any carrier, even if the phone gets unlocked from the original carrier.

All carriers in North America, The UK and most of Europe and Asia, honor carrier blacklists.

It would be useless regardless because

if the phone was off then it would of course just be a paperweight.
if you try to reset it you'd require the owner's Apple ID/password to activate it

They are useless to anyone except the real owner, due to the icloud lock system. That's separate from IMEI blacklisting.

Useless or not, anything "found" is classed as stolen property in law.

The police do not discriminate between someone "finding" an item in the middle of a forest or the owners pocket - you get arrested and charged with theft either way.

The only way to avoid that is hand a found item directly to the police.

Return that phone back to the owner ir the police you thief!