Sometimes when you're using the Crop tool (C), you change your mind and decide not to crop? Press the Escape key to cancel your crop and remove the cropping border. You can also click on the circle with a slash icon (the international symbol for "NO", image two in this post) on the far right of the Options Bar to cancel a crop. Or you can just switch tools—a dialog will appear asking you if you want to complete the crop or not- choose don't crop