I see they have an MIT license, which is great, but I have a theoretical copyright question. If they didn't license out the code and, instead, made a background

I see they have an MIT license, which is great, but I have a theoretical copyright question. If they didn't license out the code and, instead, made a background-image-generating website, who would own the copyright to the computer generated images? I'm guessing they would but does anyone know for sure?