how do i make a photo change to a sketch look

1. Open a file and create a duplicate layer by keying in Cmd+J. It is Layer 1.

2. Change the Blending Mode from Normal to Divide. The screen may go completely white. Fear not.

3. Choose Filter > Blur >Gaussian Blur and set it at 10 pixels. (This recommendation is based on a large original file. The one pictured here is approximately 12 x 9, 300 ppi. A small original (the one below was made from a 10 x 7, 72 ppi file) may produce a more heavy-handed result.

4. Create a new layer that is a composite of the Background Layer and Layer 1 by keying in Cmd+Opt+Shift+E. It is Layer 2.

5. Choose Filter > Filter Gallery > Artistic > Poster Edges. The Edge Density slider has the most effect. Set it to about 10 and click OK.

6. Change the Blending Mode to Linear Burn. If the resulting image looks too dark, use the Opacity slider in the Layers panel to reduce its intensity.

7. Click on the Adjustment Layer symbol at the bottom of the Layers panel and choose Hue/Saturation. Desaturate to -100, click a checkmark in the Colorize box and choose a suitable hue for the image. Adjust the Lightness slider for a final tweaking.

There are specialist filters such as Snap Art and the Macphun range and also you can experiment with changing the color mode to greyscale and use the Photoshop filters.