Say you have an image you want to crop the background of. Do it like this.

Trace the shape you want to crop.

Screen Shot 2017-01-21 at 6.36.02 AM.png

Then create a block rectangular mass to cover the entire thing.

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Then overlap them with eachother. Then click drag your mouse over both so they are both selected.

Screen Shot 2017-01-21 at 6.37.55 AM.png

Then select Path Finder -> Minus back to crop them.

Tada!

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Then, if you had your original image on another layer, make it visible now.

Screen Shot 2017-01-21 at 6.39.29 AM.png

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