What's to stop someone from 3D print cloning a key?

The simple answer is: nothing.

This has already been done for many years, with keys being cast or created from blanks using hand drawn copies, photographs, remembered shapes etc all being successfully used, both by locksmiths and criminals.

A 3D printed key will do just as well, if strong enough, or it could be used to cast a key if necessary, or as pointed out by @EkriirkE - you could use a torque bar to turn the barrel.

You should not ever post picture of keys to a public site, unless it is for something unimportant.

As the guys previously said, nothing!

Even more, I've been working on such a project myself at the university! (albeit I don't say this as an official target, of course)

I am trying to do duplicate a key from a single photo, with some assumptions to make it a realistic problem such as having a coin of a known size next to it for size calibration and rotation, almost symmetry between the two sides of the key etc..

My target is to automate the whole process, i.e you take a single photo and an app will detect the outline of the key and the grooves inside it (which is a really difficult problem since it's a reflective field) then construct a 3D model ready to be printed.

I have uploaded some videos of my progress if you're interested to know how things went so far :)

Extracting a key from photo

Rendering a key

Rendering of a key with its grooves!

This is the outcome

There have been a couple of researches about this in the States and Thailand, but: 1) the states': you take a photo and point out the points of interest 2) Thailand's: a reconstruction from a video-stream of the key. Meaning that none is absolutely automatic, but they're still good nonetheless.

I have also found an app for iDevices in which you can take a photo of the key and send it to a company which will then duplicate it and send it back. I have always laughed at this and said: yeah, the mailman will knock on your door and if you're not home he'll simply enter the house, put the key and leave with everything else.

Absolutely nothing.

On one occasion, a convicted killer in Australia actually duplicated a master key of his own prison cell just by looking at the physical keys carried by the guards.

He successfully escaped from prison and was on the run for 12 days before being captured.

So if a prisoner with only raw metal and a good memory can copy a key, I think that an actual photograph and a 3d printer would work flawlessly.

Every single day when "locking up my house" before leaving for work, I chuckle at how pointlessly stupid the whole practice of "keeping things under lock and key" in this day and age of technological expanse.