Xnip has rich image annotation tools. Easy to use.
Scrolling Capture - It helps you to capture a full-page screenshot even if the content not showing on the current screen. You can use scrolling capture to capture your source code, article, chat history, etc.
Window Capturing - Window capturing with the shadow effect. Furthermore, you can select multiple windows and capture all of them together.
Color Picker Tool - Pick the color of any pixel on the screen and make pixel-perfect capture.
Physical Unit - Measure objects by the screen with the physical unit size indicator of selection.
Pin Images - Pin screenshot or any image on your screen.