Watermark with prestashop
If you wish to add watermark on products’ photos, you just need to install basic Prestashop module – “Watermark”.
When you install the module, set the position of the watermark and transparency as well as choose image types for watermark protection.
Important: this module supports only *.gif format images.
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 using a tool in Admin panel > Preferences > Images.