You're making two, big incorrect assumptions:

1. Simply seeing something on the internet does not give you any legal or moral rights to use that thing in any way other than things which are, or have previously been, deemed to be "fair use" by a court of law. Individuals have personal rights over their likeness and persona, and copyright holders have rights over their works, whether they are on the internet or not. In other words, there is a big difference between "visible in public" and "public domain".
2. More importantly, something that might be considered "fair use" for a human being do to is not necessary "fair use" when a computer or "AI" does it. Judgements of what is and is not fair use are made on a case by case basis as a legal defense against copyright infringement claims, and multiple factors (purpose of use, nature of original work, degree and sustainability of use, market effect, etc.) are often taken into consideration. At the very least, AI use has serious implications on sustainability and markets, especially compared to examples of human use.

I know these are really tough pills for AI fans to swallow, but you know what they say... "If it seems too good to be true, it probably is."