Assassin - The Photoshop: Professional Retouching and Compositing Tips, Tricks, and Techniques - page 539

Figure 11.46 Drag the transform handles outside the image area to enlarge the layer.
8. Click the original render clouds layer below and drag it to the trash, and then drag
the London layer to the top of the layer stack. Click the layer mask icon to add a
white layer mask to the London layer ( Figure 11.47 ).