This page can be run offline, it is OPEN SOURCE and uses buidl.js an easy to use layer on top of the BitcoinJS library.

Create a key pair using the raw bytes of a file. It's important to be aware that this file should be absolutely unique, such as a photo you took and have never shared and has never been accessible on an internet connected device.

If you intend to use the source file as your back-up (instead of saving the resulting paper wallet or private key) keep in mind any changes to the file (INCLUDING META DATA) will result in a different key pair.
USE AT YOUR OWN RISK.