Method 3 allows for sharp and precise selections. It's also good to use because like using masks, it maintains a certain amount of the original image information.
1. Open the image in Photoshop and select the polygonal too. Set the feather to 0 pixels for a sharp selection. Begin tracing the object you wish to cut out. Holding "shift" while clicking will add to selections and holding "alt" will delete from selections. Double clicking will close the selection.
2. Once the selection is made, right-click inside of the selection and choose "Layer via Copy". Now the selection will be copied to its own layer keeping the original image intact.
3. The object is now seperated from its background and ready to be used in the illustration. This method is a little faster than the previous methods because less time is wasted erasing the background.