Hi Intervain,
It’s the most recent bottom row icon that the artist has uploaded, within the last 30 days.
So users with a big gallery but no icon under their name are either:
thanks aurick - yeah I figured it out after I made my post 
I appreciate your time 
Smashing idea!!! and a great compromise!!
Time to get sculpting!!
I’ve already seen at least one person deliberately upload an icon that has nothing to do with any posted work in order to have a custom avatar.
If you are thinking of doing this, keep in mind it pushes someone’s much more deserving thumbnail off the bottom row. People come here to view the great work that other people post here, and to get their own work noticed. There’s a lot of competition for those slots, and everybody wants their time in the spotlight. I say without a hint of exaggeration, no one cares about your avatar.
I’d honestly rather see the avatars disabled entirely, than give people an incentive to game the system for such frivilous purposes.
…for Upload an avatar at ZBC ? :o
You don’t upload an avatar. It simply takes the thumbnail of the last pic you uploaded, if you made an icon as part of the upload process for the “recently uploaded” list. It lasts for 30 days, unless you upload another pic to your gallery.
So it’s a variable avatar! 
Not easy for recognize somebody!
No, I think this is good. Anyone can go to a thread we have commented on and see our lastest uploaded work in icon form. Not that I have uploaded something yet (time for me to get working).
Besides, the bottom row icons have that “more” button and we can see all the uploads from the last several hours. I am always looking in there, and get to see much more work because of it.
I think not only does this method keep the artists latest work exposed for longer, but also gives the incentive to upload quality, not quantity as seen on some threads.
You must be misunderstanding in some way. I dont oppose the system in principle. This person uploaded an icon that had nothing to do with any work they had made (it was based on an image produced by another artist, and had nothing to do with Zbrush), just so they could have their stupid custom avatar that nobody except them cares about. Clicking on it linked to nothing, as they had presumably then deleted any display of the icon once it was uploaded to those slots.
In doing so, they pushed someone else off the bottom row thumbnails, which are worth much more in the way of click through than the extended “more” gallery. Everyone sees those thumbnails while they are up, on every visit to the site. Only a small percentage visit the extended gallery as frequently. Everybody who is interested in getting their work seen would prefer to be up there as long as possible.
I’m not saying it’s a widespread problem, but if the system proves to encourage people to do this for their own vain, selfish motivations, I’d rather see the avatar function disabled entirely. Hopefully they can tweak the system so it doesn’t reward this behavior, perhaps by deleting pics that aren’t actively displayed, something which needs to happen anyway.
Yeah I see what you mean now. Valid point. What I would hope is that the mods of the forum will come down on people for that. Though they may not have the time.
It’s always bugged me when people upload, then remove the upload and the image remains on the bottom row. If that happens it would be nice if it was removed from the bottom row too (and your avatar now) and the last person knocked off is bought back.
Sadly the system can be abused, but I do like the fact I can be chatting with long term acquaintances and check their avatar to see if they uploaded something new.
I dunno really. I like it overall.
I am sad people can abuse it, but hey, it’s just the one or two that will do that hopefully.
@dustin
I agree with you, and very much like the idea that the avatars are tied to people’s personal work, and not avatars for avatar’s sake. As such, they are tied to the same guidelines against posting frivilous thumbnails as any icon, in that we should be respectful of other artists, and not load the bottom row with frivilous images, minor updates, or have multiple images up there at once.
My objection was to someone who was circumventing that for the purpose of vanity, in sort of self interested way that didn’t respect the other artists.
And yes, I don’t expect the mods to police everything. Pixologic is a small company, and the mods’ time is stretched thin as it is. Which is why,if it became apparent this was going to be an issue, I’d just as soon deactivate the source of the temptation altogether, rather than expect the mods to have to monitor this.
I also like Avatar.