To answer another frequently asked question, the self-service functionality in the developer console that has been the process until this point in time will remain unavailable leading up to the transition to IGDB on November 17.
If you are a game developer or publisher who wishes to change the cover art for a game you own, please review these requirements, then contact developers@twitch.tv or your designated Solutions Architecture representative with a qualifying image asset. We will be taking cover art update requests via email until November 17.