PixelCryptor is a free program for Windows that protects your files by encrypting them with an image as key.
The thing that stands out about this application is the method it uses to encode files, using the information of an image or photograph. This is the only real way to unlock the files.
PixelCryptor also features an assistant for both encrypting and opening files, helping you in a visual and intuitive way.
Free for non-commercial use.