The internet is full of copyright violations. Just because you see people posting 3rd party art assets doesn't mean that they are allowed to.
You might wonder "but they didn't get sued, why should I"?
Maybe SNK hasn't found out about the copyright violation yet. Maybe they can not locate the violator. Maybe it's not worth their time because the violators don't have any money. Maybe the paperwork is already on the way. But whatever the reason why that website is still online, you have no guarantee that these reasons also apply to you. SNK can decide who to sue and who to let go for violating their copyright.
The only way to be sure that an asset is safe to use is when you made it yourself. Even so-called "free" assets you find on websites can be dangerous because it happens all the time that people upload ripped assets to such websites (some people are even so audacious that they add an own copyright notice). When you hire artists to create assets for you, you should insist on a guarantee in the contract that their work does not violate 3rd party copyrights and that they take liability for that. I experienced it before that an "artist" tried to sneak ripped sprites into a project I took part in.