Best way to create Thumbnails of images

Hi,

I need the function in my app, that the user can pick an image from the image gallery and a Thumbnail of this Image should the be stored in a Zip-File.
I have no problem accesing a stream of the just picked image through the MediaPlugin and I can write into a ZIP-File via a Stream.

What's the easiest way to get a Thumbnail image from the selected image?

All the best

Thomas