How to apply textures with alpha channel? I am doing the Introduction to Camera Tracking tutorial by Blender Guru and at some point he is applying a texture to create cracks in the road (around the hole, see image below). 



As you can see there are no cracks visible in this image. I think the problem is that I don't know how to apply textures with an alpha channel ? But perhaps it has to with the node tree in the compositor. Blender Guru is working with Blender Render, I use Cycles. 

Who can help ? Blend file with texture packed attached.

P.S I know there is also an issue with the floor but I think I can only ask one question
It looks like the ground that you are trying to apply the texture to is on the Background layer and is being used as a sort of a mask, so it is not being rendered.  What I did to fix your problem is duplicate the ground, move the duplicate in the Z direction just slightly to avoid it intersecting with your ground that is being used as a mask, and then move the duplicated ground onto the foreground layer, which you have defined as the first layer, by pressing M.


Now the ground will render.  Next, you need to apply the cracks as a texture to the new ground.  Applying textures with alpha channels is simple using cycles.  Here is the node setup that is used:

 

Now if you render your should be able to see the cracks.   

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