You have the option to easily add a border to your images. To do this:
1. Click on the Design tool in the gray navigation bar and click on your Image that you would like to add a Border around.
2. On the right-hand sidebar, scroll down and select the Border menu.
3. Click every side of the rectangle click box and adjust the attributes of your border. Use the color box to change the color of the border, and the size slider to adjust the size of the border.
4. Select Save and Publish to take your changes live!