get("#356") -- num2hex
get("#485") -- containsColor

-- Job: Distinguish two classes of images
-- Two images are supplied at once, one of each class.
-- Task is to find out if the two images are swapped or not.
--
-- input variables: img1, img2, solution [to last pair]
-- output: a function returning true or false (swapped or no)

function selectColor(img)
  local x, y = math.random(0, img.width-1), math.random(0, img.height-1)
  color = img.getInt(x, y)
end

return function()
  -- select a new color when last guess was wrong
  if solution ~= guess then color = nil end
  
  if color == nil then
    if solution == nil then
      lastimg1, lastimg2 = img1, img2
      return false -- just return something
    end
    selectColor(lastimg1)
    class2sampled = solution
    print("color of class "..(class2sampled and "2" or "1")..": ".. num2hex(color))
  end
  
  lastimg1, lastimg2 = img1, img2
  
  flag1 = containsColor(img1, color)
  flag2 = containsColor(img2, color)
  if flag1 == flag2 then
    color = nil
    return false
  end
  guess = flag1 == class2sampled
  return guess
end

Began life as a copy of #483