What is hidden on this image?

Question

Here's the image:

What is hidden on it and how was it made?

Answer 1

I got it!

First attempt:

I separated the RGB channels, XOR'd them with each other, inverted them, and arbitrarily assigned the results R=~(R^G); G=~(R^B); B=~(G^B) based on what would make the hair and skin hue broadly correct.

Result image:

The result isn't correct, but it made whatever component caused the moire patterns drop out.

EDIT: I got it!

The image is XOR'd with the function (x*y)%256.

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Final image:

Clean function:

Answer 2

This is how far I got; I created a python script to create a background image that I substracted from the given image (Update):

This is the Python script I used:

import sys
from PIL import Image
src = Image.open(sys.argv[1])
def tf(p,i,j):
  return tuple([256-(x-(256-i*j)/64*64)%256 for x in p])
odata = [tf(src.getpixel((j,i)),i,j) for i in range(0,256) for j in range(0,256)]
img = Image.new('RGB', (256,256))
img.putdata(odata)
img.save('2.png')

So it's basically the same as the accepted answer, but there is some small error in there somewhere..

And this is the correct python script using XOR instead of difference:

import sys
from PIL import Image
src = Image.open(sys.argv[1])
def tf(p,i,j):
  return tuple([(x^i*j)%256 for x in p])
odata = [tf(src.getpixel((j,i)),i,j) for i in range(0,256) for j in range(0,256)]
img = Image.new('RGB', (256,256))
img.putdata(odata)
img.save('3.png')

Answer 3

There is someone hidden in the image. I put the image here and got this: