Redirect to nitter doesn't work with pictures
You can try with this profile picture from the United Nations:
https://pbs.twimg.com/profile_images/950749155575541760/MZoiVs3G_400x400.jpg
It doesn't redirect to https://nitter.net/pic/https%3A%2F%2Fpbs.twimg.com%2Fprofile_images%2F950749155575541760%2FMZoiVs3G.jpg