In this tutorial I will show you how to add hair to a photo using photoshop. You can use this technieque to paint realistice hair on a dog, to touch up a photo that has hair to create a new hair style for your beautition or barber, or just to see how you look with a mustash.
First open up a document at the size of 150 x 150.

Create a blank layer press the D on your keyboard to set your background and foreground to default. select the brush tool and pick a 1 px hard brush and just paint a few lines ( I painted five). The style that you paint these doesn't really matter.

Now press Ctrl+A to select all, and go to Edit > Define Brush Preset. Give it a name to make it easier to find later, and press Ok. You can now close this document, no need to save anything.

Now find a photo to work with. If you don't have one, you can download the picture used for the tutorial here.

In your new document with your picture, select the brush tool and pick the brush you just created. It should be at the bottom of the list of brushes.

Click on the Brushes Expanded view and select shape Dynamics and make the following settings:

Then select color dynamics
:
Then select other dynamics:

Now we are finished creating the hair brush and it is time to paint. Select the color that you want the hair to be and pick a brush size.
note: in my experience the smaller the brush size the more realistic the hair looks (doesn't look like it was painted on).
Also, even though this is not required, I preffer to create a second blank layer and use the pen tool to trace out where the hair will be. This will give you more control of where the hair is and to make sure you don't paint hair where you don't want it. If you are using the image provided, make sure that you trace around the microphone so the hair appears to be under the mic instead of on top.

Go to the paths tab and select the load path as selection button to turn your path you just created with the pen tool into a selection.

Once you do all of this you can now start painting.
To make your hair look better, you may find it usful to change the blend mode of this layer to overlay duplicate the layer and lowering the opacity to blend the hair to the skin.
