First you need photoshop, which is Here. Unfortunately you have to make an account to download it.

Step #1.
Go to File>New


And put it to these Settings.


Now you will have a blank layer like so.






Step #2.
Create a background layer, with the color black. Then hit Ctrl+Shift+N to create a new layer. On this next layer you will be drawing what you want to be visible on your avatar.






Step #3.
Go to Window>Channels and make a new layer, if its not automatically called "Alpha 1" rename it to "Alpha 1" without the quotes. Make sure all the Rgb layers are invisible (Click on the eyes)











Step #4.
Now you need to choose the "Marquee Tool"


Go back to the layers tab, Windows>Layers


Now hold "Ctrl" and click on the layer where you want your head texture to be visible.







Step #5.
Then go back to Window>Channels and you should already have an outline









Step #6.
Select the brush tool.


And make the hard brush size about 200px or so..


Not soft Brush.







Step #7.
Now click in the middle of the picture with the "Alpha 1" layer selected.






Step #8.
Test your head out.