Working with pictures

I want to read in a presentation, change a picture in the presentation to something else and remove the old picture.

I can see how to add a new picture to the presentation and how to change the pictureID in the pictureFrame shape to the new one.

My question about the removal of the old picture.
I cannot remove a picture from the Pictures arraylist, but it looks like Aspose cleaning up behind the scenes removing unused pictures when I write the Presentation.

Is Aspose doing this or is there something else going on?

Yes, it is Aspose.Slides cleaning up unused pictures during the Write method.