You can add shape annotations in the form of straight or free-form lines, squares or rectangles, and circles or ovals.
Click the desired annotation tool button—Line to draw a straight line,
Pen to draw a free-form line,
Multi Shape to draw a few free-form shapes at the same instance, Rectangle to draw a square or rectangle,
or Oval to draw a circle or oval—and
draw the shape on the image.
Notes:
Press the Shift key to keep the straight line perfectly horizontal or vertical.
Press the Shift key to create squares or circles with the Rectangle and Oval tools.
Use the Multi Shape tool to mark a few items at the same time, when you complete drawing the shapes, click Done and type the required comments.
to draw a straight line,
to draw a free-form line,
to draw a few free-form shapes at the same instance, 
to draw a square or rectangle,
or 
to draw a circle or oval—and
draw the shape on the image.