get("#356") -- num2hex

function RSHash(img)
  local b, a, hash = 378551, 63689, 0
  local w, h = img.width, img.height
  
  for y = 0, h-1 do
    for x = 0, w-1 do
      local pix = img.getInt(x, y)
      --hash = (hash * a + pix) % 0x100000000
      --a = (a * b) % 0x100000000
      hash = bit32.band(hash * a + pix, 0xFFFFFFFF)
      a = bit32.band(a * b, 0xFFFFFFFF)
    end
  end
  
  print("rshash: a=", a)
  return num2hex(hash, 8)
end

originally from http://www.partow.net/programming/hashfunctions/ - might have different results