The Many Faces of Jane does an admirable job of presenting the few images of Jane that exist.
More images are shown in the Jane Austen Ebooks site. As you see, some of them are duplicates from the first site.
The image I’ve settled on is not my favorite, but it’s the one I see the most often: The watercolour her sister Cassandra painted in 1810. Find it at the bottom of this post on the right. See both depictions of Jane that are shown on this post here.