Name for crypto algorithm that preserves visual pattern Given some input plaintext and output ciphertext, is there a group of crypto algorithms that mean that a change in the ending x bytes of the input plaintext makes some y change at the end of the ciphertext as well? The point is to conserve the visual pattern, but to still be encrypted.
Name for crypto algorithm that preserves visual pattern

I'm not sure exactly what you're looking for, but one interpretation of your question is that you're looking for a way to 'hide' a message within a picture in a way that the picture isn't obviously changed.
The general technique to do this is known as &quot;steganography&quot;; that has the goal of hiding a message into something innocuous (such as a JPEG) in such a way that it's hard to discern (without the key) that there's a message there.  Steganography isn't an algorithm; instead, it is the general term for any algorithm that attempts to achieve this.
One common (and rather simple-minded) technique is to take the various bits of the message, and hide them within lsbits of various pixels the picture (tweaking the pixels only slightly); which pixels you use would depend on the key.
Standard joke: for more information, see the steganography stack exchange - just be warned, it is very well hidden...