I have been looking for a few ingrown feather threads with pictures, and here are a couple:
https://www.backyardchickens.com/threads/ingrown-feathers-now-with-pictures.644137/
https://www.backyardchickens.com/threads/skin-infection-on-my-rooster.1135568/
https://www.backyardchickens.com/threads/ingrown-feathers-now-with-pictures.644137/
https://www.backyardchickens.com/threads/skin-infection-on-my-rooster.1135568/