With the Gmail Screenshot by cloudHQ Chrome extension, so you can do any of the following on your screen capture:
☑︎ Write text
☑︎ Use arrows
☑︎ Pixelate sensitive information
☑︎ Include rectangular boxes or lines
☑︎ Get a link of your marked-up image to send to anyone!
To find out more about Gmail Screenshot, click here.
To install Gmail Screenshot, click here.
Instructions on how to get started are here.