This plugin allows you to add a watermark images on all images that were uploaded in your wordpress. The watermark is generated on-the-fly and cached for faster access.
To see the plugin in action, select “Add watermark to all images”, chose a watermark image and and submit the settings page. You should then see the watermark appearing on your site. You might need to reload the page (F5 in most browsers) to bypass the browser cache.
The plugin does not change your source images. To disable all watermarks, simply disable the plugin, and everything is back to normal.
If you encounter errors (especially syntax errors), check your PHP version. It should be at least 7.0. This plugin requires Apache and mod_rewrite.
Screenshots
You can select an image to use as watermark and to which images watermarks should be applied.
The settings to adjust the position of the watermark. Those are lots of numbers, but there is a (resizeable) live preview area ;-). If you are familiar with CSS, you should have no problem with this.
You can add or remove watermarks from individual images in the media library.