Step 1. Log into your PrestaShop admin panel.
Step 2. Go to Modules->Modules
Step 3. Search there for modules list named “Watermark” and click Install button.
Step 4. Once installed click on the Configure link to continue to the next screen.
Step 5. Now set the position of the watermark and transparency as well as choose image types for watermark protection (this module supports only gif format images).
Step 6. Once you have configured the settings for your watermark, click the Save button.
It inserts watermark only on new images.
If you want to add watermark on old images as well, you will have to regenerate the images.
Step 7. Go to Preferences -> Images and scroll down to the bottom of the page to the section Regenerate Thumbnails.
Step 8. From the drop-down menu Select an image you can choose the content type for which you want images to be regenerated. By default, it’s set to All. From the option Erase previous images you can select whether the old copies should be erased or not (select – Yes).
Step 9. Click Regenerate thumbnails button.
If you want to remove Watermark you will need to uninstall the Watermark module and after regenerate the thumbnails again.