I am using wordpress twentytweleve template and I notice every time I upload an image it creates 3 different thumbnail sizes. In my media settings I have already set medium & large size to 0. It seems like when I use this theme it will create the 3 different thumbnail sizes but if I use my own custom theme it doesn't create those 3 different sizes. How can I fix this in twentytweleve template?
Create child theme for Twenty Twelve and add code in How to disable multiple thumbnail generation? to functions.php