My friend just posted a picture of her key to instagram and it occurred to me that with such a high res photo, the dimensions of the key could easily be worked out.
Therefore the key could be duplicated.
What's to stop someone malicious from abusing this?
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.
