Photoshop Tutorial

Create a new document 500 x 500 pixels.
Make a new layer and fill with White:

Make sure ink is black and canvas white.
Apply Filter:
Render / Clouds

Apply Filter:
Render / Difference Clouds
Repeat 3 times (Ctrl+F)

Apply Filter:
Stylize / Find Edges

Apply Filter:
Render / Difference Clouds
Repeat 3 times (Ctrl+F)

Apply Filter:
Stylize / Find Edges

Apply Filter:
Render / Difference Clouds
Repeat 3 times (Ctrl+F)

Apply Filter:
Stylize / Find Edges

Apply Filter:
Blur / Blur More

Apply Filter:
Sharpen / Sharpen

Image / Adust / Brightness/Contrast

Finaly colourise as required

Done!