This is kind of out of the blue, and might be in the wrong forum (I remember an area for Waypoint, but I don’t know where it went). But is it possible to upload a custom avatar? I haven’t found a way, and I’ve seen people around the forums using pre-set Avatar images that I cannot find in the list, no matter how hard I look.
Also, if it is possible to update that list, can we expect a Halo 4 Warthog image soon? 
At this time, custom avatars are not something that is enabled for the general population, no. There are a few custom ones floating out there but majority are Mods/SI’s.
The Halo Waypoint forum was re-named the Halo Support forum. 
As of right now, users cannot upload their own avatars for use on the forums. There are a few circumstances in which users have been given a special avatar image, but there are certain restrictions associated with them. We usually see a new batch of avatars released every once in a while, and I remember seeing a “Create a forum avatar” thread around here somewhere, so you may see a Halo 4 Warthog image sometime in the future!
> The Halo Waypoint forum was re-named the Halo Support forum.
>
> As of right now, users cannot upload their own avatars for use on the forums. There are a few circumstances in which users have been given a special avatar image, but there are certain restrictions associated with them. We usually see a new batch of avatars released every once in a while, and I remember seeing a “Create a forum avatar” thread around here somewhere, so you may see a Halo 4 Warthog image sometime in the future!
Well thanks for the responses guys! I was hoping to upload a Warthog one myself Can’t seem to find the thread you mentioned, so I just hope they add what I want in soon!
> Well thanks for the responses guys! I was hoping to upload a Warthog one myself <mark>Can’t seem to find the thread you mentioned</mark>, so I just hope they add what I want in soon!
Try using this thread or this.