Today I was looking into a way to increase the Thumbnail size of slides in a Slide Library (MOSS 2007, SharePoint Server 2010).
The SPPictureLibrary has a ThumbnailSize property which you can set, but this is not available for a slide library. So I tried reflection on an SPList to update the related fields directly, but this only worked for Picture Libraries.
So next I reflected my way into the Slide Library Event Receivers, to see if I could reuse the code to generate the thumbnail, but found nothing except some validations.
It was only then I suspected that the thumbnail was generated during the publish mechanism in PowerPoint. And indeed so, after the publish I could find the thumbnail image inside the pptx file. However no visible option in PowerPoint controls the size of the generated thumbnail, so I guess I’m out of luck.
Too bad this is a SharePoint 2007 environment and not SharePoint 2010 with the PowerPoint Web Application :(