Click "Shadow" to add shadow to the current photo. As the picture shown below, you can change shadow position, shadow color, as well as offset, opacity, smoothness.

Offset X/Y: Drag the slide bar to change the offset of the shadow relative to the photo.
Opacity: Drag the slide bar to change the shadow opacity, from week to strong.
Smoothness: Change the edges smoothness, to make it more genuine.
Shadow Color: Select a shadow color from the drop down list.

Note: After all these settings are made, please click button "APPLY" to confirm setting. If you want to remove shadow, please uncheck box "Set Shadow" and click "Apply".