bulkWaterMark is based on PMlabs GrfX, our own framework for image processing software. Therefore bulkWaterMark supports expanding its feature set in many ways. The app can be extended by using a Microsoft .NET language of your choice with new layer types and expressions for your watermarks and image format readers or writers to support more image formats.
Although our first GrfX-based product bulkWaterMark is already released, we are not supporting the development of custom PlugIns yet. All bridges and connections are implemented at the moment, but we are still working on polishing the interfaces and documentation of the PlugIn system.
We will officially release the SDK in early 2016. Please stay tuned! :)