If someone used something that I created and didn't give me credit for it, I'm sure I would be upset. I would feel that they actually stole from me. I'm not particularly fond of thieves so I would definitely want to see the person that wronged me brought to justice. I would also want that person to publicly admit what they had done and then give me proper credit for the actual creation. If someone had accidentally taken credit for something that I did, I would also ask them to publicly admit their error. I would not want them to be legally punished if they had simply made a mistake. I feel the same way about accidental plagiarism. If someone does not intentionally plagiarize then I don't feel that they should be treated harshly.