get("#380") -- hashImage

w, h = img.width, img.height

function cacheImage()
  cached = {}
  for i = 1, 100 do
    local x, y = math.random(0, w-1), math.random(0, h-1)
    cached[i] = {x, y, img.getInt(x, y)} 
  end
end

function hasMovement()
  for i = 1, #cached do
    local x, y, pix = unpack(cached[i])
    if img.getInt(x, y) ~= pix then
      return true
    end
  end
  return false
end

return function()
  if cached == nil then
    cacheImage()
    return nil -- "Initializing..."
  end
  if hasMovement() then
    cacheImage()
    return "Movement"
  else
    cacheImage() -- optional, but a little safer
    return "Probably no movement"
  end
end

Began life as a copy of #467