BuddyPress.org

Do you want this picture as group logo ? Or to just display it on a group page ?

BP components pages should stay blank, without any page setting like normal WP pages.
It works on bbp because it’s a “real” static page which let you also handle bbp output with shortcodes. BP pages don’t work like this.

There was also a kind of experimental plugin in the past:
https://github.com/hnla/buddypress-group-branding/blob/master/inc/bp/bp-bgb.php

Other option (premium):

BuddyGroupHeaders