GroupDocs.Watermark API supports adding the following image file types as image watermark:
BMP;
PNG;
GIF;
JPEG.
Add image watermark from local file
The following code snippet shows how to add ImageWatermark to a document. If the document consists of multiple parts (pages, worksheets, slides, frames, etc.), the watermark will be added to each of them.
// Specify an absolute or relative path to your document. Ex: @"C:\Docs\presentation.pptx"using(Watermarkerwatermarker=newWatermarker("presentation.pptx")){// Use path to the image as constructor parameterusing(ImageWatermarkwatermark=newImageWatermark("watermark.jpg")){// Add watermark to the documentwatermarker.Add(watermark);watermarker.Save("presentation.pptx");}}
Add image watermark from stream
You can also use a stream of the image to initialize ImageWatermark instance as shown in below example.
// Specify an absolute or relative path to the watermark image. Ex: @"C:\Docs\watermark.jpg"using(StreamwatermarkStream=File.OpenRead("watermark.jpg")){using(Watermarkerwatermarker=newWatermarker("image.png")){// Use stream containing an image as constructor parameterusing(ImageWatermarkwatermark=newImageWatermark(watermarkStream)){// Add watermark to the documentwatermarker.Add(watermark);watermarker.Save("image.png");}}}
Warning
The ImageWatermark class implements an IDisposable interface. Therefore, it is necessary to call the Dispose method when you are done working with the watermark. Alternatively, you can use the using statement.
For the advanced use of image watermark properties please check the following article about text watermarks, however, the same techniques will work for image watermarks as well: