You can upload a watermark logo from WPL->Settings->Gallery and configure its options for showing branded images on the frontend of your website. The WPL watermark feature adds a watermark logo to the thumnbail and keeps your original image clean. You can change the watermark logo or deactivate it whenever you like.

For uploading and configuring your watermark logo, go to WPL->Settings->Gallery:

You can change the Watermark status, position and opacity using Watermark options easily.

Then enable the watermark option on gallery activity:

Before checking the frontend, you should clear the listing thumbnails or set the Rewrite option of gallery activity to "Yes". Removing listing thumbnails is recommended.

To complete this action, check the frontend of your website.  You will see that the watermark is added to the image.