Step one: I created a sketch, which was imported into Photoshop (CS4). I then created a mask to paint on the image. I randomised the sketch using the charcoal filter (thickness 1 / detail 4 / balance 73), and the pencil tool (disolve opacity 100%).
Step two: Painting in the background. I chose not to mask out the horse, but painted it in with the background. For this I used a watercolour brush with 100% opacity and 70 flow. I then accented the edges (edge width 2 / Brightness / 38 / smoothing 5). I then used the cut out filter to break up the strokes (levels 6 / edge simplicity 2 / edge fidelity 2).
Step three: Adding the rain effect, contrast, and rest of the background. For this, I created a new mask for the horse, and used angled strokes (direction balance 50 / stroke length 15 / sharpness 3). For intensity I used the dark stroke filter (balance 5 / Black intensity 6 / white intensity 2). For more contrast, I created another mask and intensified the image further with the sumi-e filter (stroke width 10 / stroke pressure 2 / contrast 16). Finally, I added uniform noise @ 12.5%.
I decided to leave it there. Obviously, with the tools available in photoshop, it is tempting to work and re-work an image. Sometimes less is more though, and I think I managed to achieve the effect I was going after with this project.