link from the replies; large parts of the information in this post are incorrect.
full text copied & pasted below, source links available in original link:
It's an app on Discord. Anyone can create an app. There is nothing special about DomoAI besides having access to the "Edit Images with Apps" button you can see on uploaded images. Any app anyone makes can work like DomoAI does (besides access to the edit images button).
It's NOT partnered with or made by Discord. The app got featured in the App Directory and hand-picked to be in that "Edit Image with Apps" button.
You MUST add the app to your account or to a server to use it. It is NOT "in every server but sneakily don't show up in the member list". If you see the app used somewhere it is because someone added it to their account or to the server.
Even if you see it on the "Edit Images with Apps" button it does NOT mean that you or the server have the app installed. If you try to actually run the command it will prompt you to add the app before you can use it.
It can ONLY see images if you run a command on the message or mention the bot in your message*. It CANNOT scan every message unless someone is manually running a command on every message. See Message Content Intent for details.
* The bot can only see messages its been mentioned in if it has been added to the Server.
They (DomoAI) claim they don't train on artwork or images the app is used on. Whether you believe that or not is up to you, but Discord took down Shapes Inc. for training on user messages. I wouldn't recommend giving important images to random apps you don't trust anyway.
Apps do NOT have the ability to re-add themselves to a Server or to your Account after being removed/de-authorized. You have to explicitly and manually re-add them yourself if you later want said App back.
Discord's "Remix" feature is completely different to the "Edit Image with Apps" feature/button. Remix is a mobile-only feature where you can manually edit your images with basic tools (like cropping, rotating, adding text, etc) and has NO AI functions in it. All Remixing is done on your device.[Citation Needed] You can read more about Discord's Remix feature here on Discord's Support Article.
What you can (or cannot) do:
Banning the App does NOT disable anything. People can still use it if it's added to their accounts and admins can still add the bot to the server.
Disabling "Use Application Commands" and/or "Use External Apps" permissions does NOT prevent people from using it; it instead makes responses ephemeral (only visible to the person using the app).
Furthermore, disabling "Use External Apps" permission does NOT prevent usage of Bots/Apps already added to the Server (they are NOT external Apps if added to the Server after all). Disabling the Permission only affects User Apps added to accounts.
Please note: Disabling "Use Application Commands" permission will also affect usage of Bots/Apps added to the Server. (Namely, Slash & Context Commands from said Bots/Apps)
You CAN Right Click/Long Tap a message > View Interaction Info to find out who called the command and then ban/warn/etc.
Linking to an image instead of uploading it does not show the "Edit Images with Apps" button.
Finally, a note about how Server Bans work:
It has always been possible to ban someone from a Server via their User ID, even if they aren't in the Server at the time of the ban.
Just because a Ban was successful doesn't outright mean that user was in the Server at the time. It just means you successfully added them to your Server's ban list, regardless of their existing presence in your Server or not.
Plus, Discord does not check if the user you are banning is already banned from the Server or not. So, bans may still act as successful even if already banned.
In other words: Just because a ban of the same already banned user was 'successful', doesn't mean they snuck back into the Server. It just means Discord needs to add a check to add a message stating the user is already banned!
