A png is about as much code as a compiled binary. They aren’t code, they might be the result of some code being compiled, but open source licenses normally define the source as the format most useful for editing, which probably is the input that a png icon is generated from, not the png itself.
I am not entirely familiar with the .psd format. However, a rule of thumb is that if you can open an image file in a text editor, see readable code, and modifying the code affects the image, then the image is definitely written in code.