To crop an image after adding into design area, just click on image and select crop tool
The new popup show up
The image will be cropped with the exact position you put into the viewer.
There are some tweaks to make your image align better such as:
Center: move selection to center of image
Horizontal center: move selection align to horizontal center
Vertical Center: move selection top align to middle
Square: make selection square
After selected area, just press Save button