By Jake Redekop
Vector Masking allows one to hide parts of a layer.
Duplicate your image (right click and choose ‘Duplicate Layer’). Now, create a new layer by clicking the ‘Create New Layer’ icon located at the bottom of the layers palette. Fill this new layer with white using the Fill Tool (shortcut: 'g') and move it down one position on your layers palette. Select the top layer (your image) and apply a vector mask to it by clicking this icon: also located at the bottom of the layers palette.
While the vector mask is enabled, anything painted black will be hidden, revealing whatever is behind the layer (in our case, a white canvas) and anything painted white will be visible.
Click on the vector mask and select the brush tool (shortcut: 'b'). Now, with black selected as your foreground color, start painting on areas of the image that you wish to hide. As you do this, you will reveal the white canvas from the layer immediately below your image layer. If you accidentally hide a portion of the image, switch your brush color to white and paint over the mistake. To quickly swap the colors in your swatch, hit the 'x' key. This makes correcting mistakes quick and easy.
Some helpful tips and shortcuts: magnify the image with the Zoom Tool (shortcut 'z') for more precision. While zoomed, press and hold the space bar and left mouse button, and move your mouse to move to other areas of the canvas quickly. Use the '[' and ']' keys to increase or decrease your brush size so as to make getting in those tight spots easier.
Tip: Try using a brush with 50% hardness to smooth any unnaturally rough or discolored edges of your subject caused by the masking process.