Why won't iPhone screenshot open in Linux Mint?

Question

ubuntu

Hello. Faced such problem: periodically clients send screenshots made in iPhone in png format. Such pictures, for some reason, flatly refuse to open in my Linux Mint 17.3. More precisely, they can only be opened in Gimp.
In principle, this is not very annoying, but it is very interesting why this happens?

Answer 1

Because it's a jpeg with the wrong extension.
After changing to .jpg it opens normally on Xubuntu. The problem is not Linux.