Is it ok? Can I just resize them and sell here if nobody done that before me?
I will give credit for that textures. I don't earn money so it isn't piracy, but I want an admin or moderator to judge it.

Only people who done this, who are administrators or moderators are asked for answer. Only they should write here.

It depends on the game. Some game art work is protected by copyright so using it is a no no.

Open source games are generally ok.

What the f do you mean?
like if you take other textures or textures from other GAMES like for example halo or counter strike ?

[EDIT]

Damn skulfuk got here before me >_<

Skulfuk - So if only software is protected by copyright I can sell this heads?

Basically if the game is commercial, or has a copyright on it then you can't.