Hi Tony,

re:
> In practice, as I understand, you have to insert a geometry drawn in MOI and exported to Obj
> for example and he creates a flat square image where you then create the texture with a
> photo editing program? .... or does it work differently?

Yes that's basically it - the UV mapping generates a 2d coordinate value for every polygon vertex to control how a 2D texture image will be applied onto the polygons.

The tricky part is avoiding the image getting stretched out or compressed in different areas.

For chunks of dirt like you want it may be better to sculpt those in using 3D Coat or ZBrush though.

- Michael