Step 1: Materials
1 Photo of a subject. I kindly asked my Totoro stuffed animal to pose for a few shots. Having a couple of pictures from different angles is optimal, but not necessary.
1 Hi resolution background picture. This should be something scary like a forest, a dark alleyway, or another place where you could picture zombies. The image does not have to be scary, as I will show you how to tweak it in photoshop. I found my example picture here: http://1.bp.blogspot.com/-4qCy09Nn_2Q/Tl0Yc_ViDII/AAAAAAAAAig/3I7S1ofLv4g/s1600/allegheny-national-forest-pennsylvania-wallpaper-1600x1200-forest-wallpaper-nature.jpg
1 Picture of a gun of some sort. I found mine here: http://www.airsoftnews.fr/wp-content/uploads/2009/03/tokyo-marui-m16-golgo-13-ve.jpg
1 Image of another zombie-hunter weapon. I found a baseball bat here: http://m.baseballrampage.com/p/productphotos/PLC271_TPX_display.jpg
Some silhouettes of zombies. These worked well: http://img.coplusk.net/originals/0010/8474/zombie1_1265330868.jpg
A muzzle flash: http://img227.imageshack.us/img227/8817/muzzlef3xk0.jpg
And about 20-30 minutes of your time.