PNG Merge

How many images in this PNG?

This is a Poc (Proof of Concept) to create a PNG file that contains different images somehow entangled together.
The original idea is from @reversity who proposed us a hand-crafted PoC.
There was no available script to play with so @angealbertini and I tried to reverse-engineer it :-)
The idea is that PNG data can be interpreted depending on the Color Type among other types as RGB values (color type =2) or as indexed values (color type =3) together with a palette (PLTE).
RGB PNG (color type =2) can legitimately contain a PLTE, from the specs:

If present, it provides a suggested set of from 1 to 256 colors to which the truecolor image can be quantized if the viewer cannot display truecolor directly.

Which means nowadays that a PLTE in a RGB image will be systematically ignored!
So just by changing the color type byte (typically the 25th byte) from 2 to 3 (and the IHDR CRC) we can change completely the way the image is displayed.