In this tutorial I'm showing a very fast way to turn a normal image into a zombie image. This technique could be useful for posters, album designs, etc...
1.Open your desired picture. Here I used a picture of my friend taking a good zombie position.
2.Make a Hue/Saturation layer with these following settings and blending mode :

*It's starting to look like a zombie already. You can stop now or on any of the following steps.
3. Duplicate your image and move it to the top, Make a new Hue/Saturation layer with the following settings (you can play around with them) :
4.Merge the top two layers by linking them and pressing Ctrl+E . Change the blending mode to overlay and opacity to 50% .
5. Make a new empty layer. Set it to overlay. choose a soft black brush (or a grungy brush) and start brushing some area in the face or any place you want.
6. Make a new empty layer again, Get a grungy brush. You can download the one I used from here :
Grunge Brushes 007 - Free Photoshop Brushes at Brusheezy!
and just use it and erase unwanted area.
Again, all the steps from 3 to 6 are optional.
Here are my final results :
I hope you liked the tutorial.