A clipping mask is an object whose shape masks other artwork so that only areas that lie within the shape are visible—in effect, clipping the artwork to the shape of the mask. It is a useful way of creating the look of "cropping" an image without having to move into Photoshop to create a true crop.
Follow the steps below to create a clipping mask around a portion of an image.
1. Bring an image into Illustrator. You can do this by Going to File > Place and selecting your image, or by dragging it from your Desktop into Illustrator.
2. Set your colors to a black stroke and no fill.
3. Select the Rectangle Tool.
4. Click and drag to draw a rectangle around the area you want to be revealed by the mask.
5. Your rectangle will be automatically selected.
6. Choose the Selection Tool.
7. Hold the shift key and click on your image. This allows you to have both your image and your rectangle selected at once.
8. Go to Object > Clipping Mask > Make.
9. Your image is now masked!