Brief: An attempt at encoding messages using particular pixels of an image.
Given a key K, override particular pixels of an image to hold characters of text. Using the 256 possible values of the red, green and blue values of a pixel, respectively, one may fit a block of 4 characters of a 64-letter alphabet in a single pixel.
Zero-index the image's pixels from top-left to bottom-right, row by row. Let N be the number of pixels present. Choose K as a number coprime with N, and some initial offset I.
The j-th block of characters may be found in the (I + j*K) % N-th pixel. Signify the end of a message with some decided character. A maximum of N blocks of characters may be encoded with this method.
The key K must be coprime with the number of pixels N to ensure no collisions with already-encoded pixels in the encoding process.