You are wrong: the law of trademark and copyright does not have anything to do with handcrafted vs. mass produced: you an no more legally create a single handcrafted copy of a copyrighted or trademarked image or character (or an adaptation of a character, like making, in your example, a Disney-princess-inspired magnet). If something is trademarked and/or copyrighted--and any known character, etc. will be--only the rights owner may reproduce, adapt, sell, etc. it.Also do not conflate trademark and copyright on the hand with plagarism on the other; giving credit does not make a use of a copyrighted or trademarked image or character legal.The laws are the same about any trademarked, etc. character, symbol, graphic, etc., so those for mascots, cartoon characters, logos, etc.The only images created by others which you can safely use are those which have been deliberately made available for use by others.