Is it possible to choice where in a photo/doc to put the watermark? As I can see it it is default in the center.
Aspose.Words watermark app is developed on top of Aspose.Words for .NET back-end API. And the API allows you to set watermark alignment/position. Please have a look on this documentation article.
However, we have logged a feature request (setting watermark position using web app) in our internal issue tracking system with ID WORDSAPP-140. You’ll be notified in case of any update.