I'd like to create an image viewer in C# with multiple image (file) format support (not only the regular formats like jpg, bmp, gif and png) and also a possibility to create a thumbnail view. No other image processing necessary!
Who can give me advice about (free) components, libraries or .... ?
Well a search for ".net image library" turned up several possibilities including:
http://freeimage.sourceforge.net/
http://sourceforge.net/projects/openil/
Check out their file format support and other capabilities.
There's a method on the Image class GetThumbnailImage that will create a thumbnail for you.
This is a very, very tall task, and I'm not sure why you want to go about it. There are several browser plugins available for purchase that can do this for you. But if you are insistent on doing it yourself, you are most certainly going to need one ore more flavors of GhostScript.