Thanks. To create the actual sketch I followed a part of a tutorial I copied some time ago from www.photoshopessentials.com by Steve Patterson.
1. Duplicate background layer 2. Press Shift+Ctrl+U (Win) / Shift+Command+U (Mac) to remove the colour. 3. Press Ctrl+J (Win) / Command+J (Mac) to duplicate the desaturated layer. 4. Invert that layer by pressing Ctrl+I (Win) / Command+I (Mac) 5. Press Shift+Alt+D (Win) / Shift+Option+D (Mac) to change the blend mode to Colour Dodge. 6. Go to Filter > Other > Minimum. Experiment with the Radius value. For this one I set it to 15 pixels and click OK to close out of the filter's dialog box. 7. Press Shift+Alt+Ctrl+E (Win) / Shift+Option+Command+E (Mac) to merge the layers onto a new layer above the others.
Then I dragged a torn paper mask onto the document and placed it below the composite layer created at step 7 and clipped the photo to the mask and added a drop shadow. Turn off the Black&White layer and the Inverted layer and then put a hand in place using a layer mask and brush away the parts of the hand you want hidden behind the mask and that's it.