The Screen editor tool is a part of the Image editing mode. Here, you can specify the visible part of the screenshot (i.e. to crop the picture). This is extremely helpful when you want to crop a large image and display only a certain part of it. Drag the sides of the red frame to specify the visible part of the screenshot.
You may also add text labels to the screenshot. Text labels are independent objects that you can edit, move, and delete. For each label you can specify the border. This allows creation of ovals or rectangles over the particular parts of the image.
Text label toolbar
Use this toolbar add, show and delete text labels.