Thank you for using Just Answer.Under copyright law, the standard for infringement is “substantial similarity.” Substantial similarity means an average observer would recognize that the second work takes copyrightable authorship from the first one. So the first question is, what is copyrightable authorship? With respect to pictorial or design elements, copyright covers “expression,” that is, the artistic choices made in expressing an idea, but not the underlying idea itself. For example, more than one illustrator has depicted the idea of a figure removing part of his head along with his hat. However, there is no infringement when the artistic decisions used to depict that idea are different, e.g., different postures for the figure, different composition, and different rendering styles. Copyright infringement
occurs when your new work incorporates artistic expression from the original, even if it takes only a small part of the original work, and even if you add a lot of your own original expression. For example, if the second illustrator rendered the same figure in the same pose, removing the same hat, even if his illustration has a different background. There is a famous quote from Judge Learned Hand that goes “no plagiarist can excuse the wrong by showing how much of his work he did not pirate.”If a person could look at your mouse ears and have a good idea where the idea came from, chances are very good you are looking at infringement. And the "mouse ears" are so well known as an item produced by Disney and sold by Disney online and in the Disney parks that they're recognized almost worldwide. You might have people tell you or you might have read that if you change the design by a certain percentage -20%, 50%, 45%, whatever --that it makes it okay. But there is no such law. And when you think about it, how could you ever assign a percentage to something like artistic design and expression? So, I think by selling them, you're putting yourself at risk. Now, do people do it anyway? Sure --look on sites like Etsy, and you'll see tons and tons of products that people make that run afoul of copyright and trademark
ownership. Those people simply haven't been found yet. But a company like Disney has people looking for such things every day, so really it's a matter of time before they're discovered. It's possible that if you sold online that wouldn't happen for a long time. It's possible also that you might just get a letter to immediately cease and desist selling online. But it's equally possible that they sue you for damages they believe you've cost them by selling. My opinion is it's not worth the risk, ultimately. If you need clarification or additional information, please reply and I'll be happy to assist you further.