Part of me is curious to what people would do to my characters. Like if I had the ungodly ability to keep track of every or if any is in use / stolen. Then pop in and correct all the behaviors they were trying to role play my characters in. (Like spying on their every move.) Being on the internet and in chat rooms frequently I'm easily very annoying. If they couldn't escape me I would most likely drive many away from my clan weirdos. But that is not an option. Though trolling the troll in my methods have proven most want nothing to do with me after they challenge me. I have no such power to inflict on the invisible so its all for not.

Though before I ramble, to get back to the question. I feel a bit mixed up about it. I realize some on the younger side do not fully understand what they do or how they are truely effecting the owner of the character. Most would think its harmless fun not thinking about the consequences for themselves and the artist. Though that is a small excuse to many who would read this. Them yelling in many artist's faces its free cause it was on the interwebs. Crushes that idea quicker then a landfill on a mouse. I feel those who have uttered that statement have not contemplated much outside themselves to even grasp the artist's pains. The concept loses them as they have not developed enough to even begin said thoughts. (Even some adults cannot think outside themselves.)

I've seen blatant art theft mostly on rp related sites. It's quite off putting to see as an artist. I had no idea rp existed when I was a child so I wasn't in their shoes. Though I can kind of see it. Your little, your broke, most use internet as a private escape, and even most not supervised by parents. I know I try to be an understanding person but if I found someone had used my babies in lewd acts I'd be furious. I don't care if my friends do it because I know they wouldn't steal and rip their souls from me.

Art no matter if its a commission is part of our soul, our mind, and our beating hearts. We create things that show tiny reflections into ourselves. When someone takes that tiny reflection and changes it and abuses it. Putting myself in that shoe I could only think of tears. It would be like setting a fire to a painting you slaved over for weeks and even months. To have all the work and even emotional attachment burnt up to ash. Our characters are our wittle fictional babies. If any of mine were living and breathing they be spoiled rotten to the core like little divas and princesses.

Though its that fire that makes me hate theft. I wish the concept that art isn't this free thing in life. Though at the same time. I try to believe in some of the old gizzards. The wisdom that in some realm the art we create is our standing moment where we can make a mark upon the world. To be remembered and even admired years after we are dead. Other professions do and don't have that opportunity. Though I feel as a collective mind we kind of share that somewhere together. (Most I would think?) But a concept I learned, people on a level create things so other's can enjoy them along side the creator. I feel its a dyeing concept but also it's an abuse concept now a days. When people rip it from the hands of the creator for their own person merriment. The line has to draw somewhere in the sand. Yes we do share this piece of ourselves in hopes you enjoy or even connect on some emotion or physical level to us. I feel in a way it's what happens to the old gizzards paintings. Art collector gather them up and make their own private collections. Even when the artist's whole life they wanted to share the beauty they created to the world and not someone.

I understand how frustrating it is to have something you made or own, stolen and used without your permission...
I could imagine it's much more painful when that something is dear to you, and represents you online, as if your own body.

OCs or original characters are tricky. Because there's a chance someone out there, coincidentally, has a character that looks similar to yours. These chances increase the more simple the design is. Which creates issues, with people accusing one another of stealing their "oc", even if the design is super simple.

However this isn't to say people don't steal art, and literally copy other people's characters, or online "avatar"...
A lot of it has to do with people feeling "entitled" to everything on the internet. They think everything should be free.
They feel as if there is no repercussions to them, and no consequences to others.
"If it's on the internet, it's already free", and "I don't need to ask for permission" or "I can do what I want, if I just credit you"

This is even worst when people pirate from small business, groups and people. Such as authors, artists and patrons.
Who work hard to survive, maintain their careers and reputation, OR support creators and the arts.
People don't seem to understand the importance of copyrights. They should be grateful that others-
are willing to share pieces of themselves, and their work, online.

Having people pretend to be you, your character(s) or "avatar" sucks.

Because then you have to deal with the bullshit, that comes as a result. Such as strangers contacting you...,-
OR people attacking you for things an impostor did, somewhere else online.

I think the best way to discourage art thefts and impostors... (other than reporting or taking it to court)
-Is to upload art at a low quality, with watermarks, signatures with links to your main account.
(some where- were they can't crop it out)

-Keep character references private, and restrict most character (or personal art) to friends only.
(starting groups or things like that may be helpful in sharing art and stopping "drive by down-loaders")

-Then last but not least, secure your name or alias at sites that are important to you.-
Make a contact list of where you're online, "officially".

I'm glad you're taking a stance against art thieves and impostors-

who commission or steal art of other people, or their character(s) and avatar.

However that's going to be difficult to achieve, because of how vast the internet is and how numerous people are.
I can't think of any solutions that work best. The only thing that comes to mind is "reverse google image search",
digging through character submission and refs. OR asking people around the net. Which can be time consuming...