Re: BUMP MAPPING
I used Photoshop, but it can be done with gimp as well. This is actually my first normal map, but I've done few bump maps before.
Last step before you create a normal map, is to create a bump map (for simple tile textures).
Bump map is gray scale image, where higher things(tile) end up whiter, than lower things(fugues, cracks).
Fortunately in your texture tiles are placed perpendicular and selecting them was easy.
Next thing what I did, I simply selected tiles and erased them (filled with white).
After that was done, convert image to gray scale (desauturate image).
At this step you can adjust brightness and contrast of fugues and cracks.
Then I selected white tiles and applied some (Gaussian)blur, so edges look bit softer.
(On image increased contrast and blur are hardly noticeable).
And this is it. This is how bump maps look like.
Now you just apply normal map filter and you should end up with similar results.
(Its not perfect because there are still many small things you could improve, to make it more "realistic"... But that would be too much to explain)