"Fair Use" as many sprite Authors bring up IS a real copy right law. However for something to be Fair Use it a.) has to be part of the public domain (all non copyrighted images and or images so famous that it has been proclaimed as public domain (like the Mona Lisa for example), and or Educational use of said images. Sprite comics piss me off when they claim Fair Use protects them cause it doesn't protect a god damned sprite ever created since sprites are too new to be public domain. However, game companies usually will not form litigation agains use of their sprites since they view them as insignifigant as far as yearly returns on said images goes.
You CAN say you're just practicing...but for such a medium to truly be considered educational you cannot make money on it, display it in any non educational enviroment, or pull any noticable amount of money traffic from the owner of said copyright (Say if I made a picture of mickey mouse having sex with a woman and Disney's sales went down because of it...which is hypothetical).
Giving credit to the author does NOTHING. Aboslutely nothing. Now if you WRITE the author and get a legally signed document (notarized perferably) of them saying you can use their document then you're good to go. Most author/creator's require you to give them credit on the document as well which is why you SEE people giving them credit. But I assure you they have legally signed documents to back up they had permission to use the images before accrediting it to the author.
[22:38] <DJ_Cyni-Cole> you're tell me, a writer, that books are lame?
Jesus fuels with 89 Octane and so do I. Eat it, heritics. -Halo