How about have an avatar for each channel?
remove edit channel header, remove edit channel purpose, remove rename channel
and create a new dialog screen called Channel Settings with
channel name (channel avatar)
now if its a question of size or permissions I suggest to create a change channel avatar option and a simple dialog with channel name and the avatar where the user can click a change the image.
in the Edit Channel screen, set avatar icon on the right next to the channel name.