I hired someone to help me do some photoshop work. I told them to make screenshots for my game. I also gave them a picture where they have to change the items in it to look like the same object as it is but to look differently. How would I know whether or not the person used images from the web that are copyrighted? I know I could tell him not to, or ask if he has, but the person would still be able to without my knowledge. Are there any ways I can protect myself against a possible lawsuit? Does changing a picture using photoshop free you from any liability?
My feeling is that the best way to assure that you aren't violating copyright is to provide the designer with photos which you know are safe to use rather than asking the designer to do the research for you. Or similarly, tell the designer that s/he must use photography from a licensed stock site, or provide you with a source file and a copyright release from the originator.
While I'm not a lawyer, I'm fairly sure that "I didn't know it was a violation of copyright!" is not going to get you off the hook in court.
Interesting question. I my practice I faced with two companies which asked me about my liability insurance. They not hire service providers without such insurance in all.
In other cases the special Agreement can be signed between you and service provider about liability for copyright issues.
Own graphic object that looks differently from initial or prototype is hard to claim as violation of existing copyrights. But, for sure, it depends how different and similar prototype and final result.
To answer your first question: I would definitely use the google reverse image search to see whether you can find similar images on the web. http://www.google.com/insidesearch/features/images/searchbyimage.html
For your second question: Make them sign a disclaimer. It could read something like "We hereby declare that we generated the delivered graphical content ourselves and did not violate any copyrights". If you get sued, you can sue them.
For the third question: No. Editing a copyrighted picture without the copyright is forbidden. http://www.ehow.com/facts_7589563_can-edit-copyrighted-picture.html