How do I get my image to use Alpha in Cycles.
SOLVED: I used a mix shader. Here is the node setup.
This might help:
http://blendernerd.com/alpha-mapping-in-cycles/
I use the following setup
Attachments
2 ways to do something. Nice
Thank you so much blendercrazy, this is exactly what I need. I have been struggling with this for so long. I was simply trying to
apply a decal in Cycles and your setup made it work ! YEAH!
The first solution allows to put a différent texture behind the first mask. The second is much better for à leaf for exemple when the texture had already a alpha channel. I went for posting my researches and I realized that they were already done !
I post my result just in case 
Edit : I didn’t understand what you were surching for ! Excuse me, I am a poor french and so it’s a little bit difficult to understand the whole purpose (And I didn’t watch the first picture before answering ! This don’t helps !).
Then, a third solution to do alpha mask with cycles !