What's ImageFish? It's a program that lets you encrypt text files, using Twofish encryption, and hide it in an image file.
It uses a SHA-256 hash, generated from your password, encrypts the data and stores each bit of the cypher in the least significant bit (LSB) of each pixel's channels' value. To the human eye this change is barely (if at all) visible.
It also supports storing key value pairs. This is usually used for passwords which are automatically copied to the clipboard if the pair is selected.

Get it here.