Inside the image is the code that created the image.
Each pixel's R G B components are 1 byte each of the file the image represents.
pixel11Red=byte 1, pixel11Green=byte 2, pixel11Blue=byte 3, pixel21Red=byte 4, pixel21Green=byte 5, Etc.
The content of the image is a php script that generates images, via the GD library, of the chosen files which are selected by changing the variables in the script.