Don't see a reason why that should be complicated. This is a thing of maybe 1 hour or less without any kind of big board optimization and UI integration. @Alfa1: There is a dedicated Avatar service in the core - you would just need to call that for all Users of your group with their already set avatar and then use the update function.
Edit: Whoops, just saw the 1.5 tag. I'm talking about 2.0, haven't looked into 1.5.