i just found a texture that fits my character perfectly off the internet, but i didnt buy it from anyone. Would that count as plagiarism?

Yes that counts as plagiarism. There are free heads out there such as on these threads

http://forum.toribash.com/showthread.php?t=114379
and
http://forum.toribash.com/showthread.php?t=565971

"the practice of taking someone else's work or ideas and passing them off as one's own."

Now, if you're trying to sell this artwork, it's plagiarism. If you're wearing it, it's not necessarily plagiarism if the artwork is royalty free (aka anyone is welcome to use it).

I don't think there's any specific rule on the forum for using some artwork from online as a head texture, but I may be wrong. I'm sure a smod would be able to give you a definite answer.

If you're just wanting to be safe though, be sure to check any copyrights on the art. If you're 100% sure rthat the art is free for anyone to use, feel more than happy to wear it my man. If you somehow mess up, no one's hear to bite your head off (except maybe skul; he might bash your skull in); I'm sure if any mistakes are made they can easily be cleared up. (:

Some heads you may see in "Internet" May have water marks so you can identify if they are free or not. As Than$#tos said all free textures are in those threads.

Please, dont google images on the internet for head textures.
search on the forums domain to check if it is free or not.
I put sometime an artwork online for someone to download and I dont trust google for safe free heads

If you see a random head on google image search it's not necessarily a free head, it might be leaked, but still belong to someone else.
If you see a free art on toribash forums in one of those "free to use art" thread, you can wear it for free on your tori, however you are not allowed to try and profit from it in any form. That means you are not allowed to sell it or alter the image and then claim it as your own.