on youtube you could just lie and say you bought out the said copyright, for example saying: I paid such&such with so&so ammount of money to use this. If not, you can use only 20 seconds of a song and it's not illegal, or use uncopyrighted loops from a software to make a remix of a song, in which case dj's break the law all the time because the software can cause you to be able to make the remix. Also, for pictures, if you are not making profit IT SHOULD NOT BE ILLEGAL so long as you credit said artist. However, for brushes, you could also lie and say you somehow made the exact same thing, though it's hard to believe. If you download things like songs or videos from a website and give credit to the site, the government can't really do much except close down the site. For example, my any video converter stopped working for youtube videos because there have been too many copyright infragments on similar programs.
my whole opinion on copyrights like brushes or inspiration, THE GOVERNMENT NEEDS TO STOP WASTING THEIR TIME AND MONEY BECAUSE IT'S GOING TO HAPPEN IRREGARDLESS IN MOST CASES.