This behavior insert a watermark image after the upload and the resize process are completed.
The upload process, after is completed, verify if this behavior is in the page and if the behavior is find add the watermark image where setup
If one or more watermark image are void the behavior skip the image and don't add the watermark to this image. So you can define if add the watermark to all the images or if skip one of them.
The watermark image must be on the site, is not uploaded during the upload process. You must put the watermark image in the site.
Click on the browse button to select the image you want use like watermark
This behavior to work need the Asp.Net Framework installed on the server