I've recommended Windows' built-in 3D Paint for background removal before — most of my covers are cut out there, then edited further in Gaoding. But when it struggles, try ImageMatting, a free open-source matting tool.
It supports single and batch removal with one click, and you can fine-tune afterwards. It can also generate ID photos: set the size, press play, and it auto-cuts with a transparent background by default — switchable to white, blue or red.
ImageMatting also converts image formats and compresses images (needs a TinyPNG key; for compression I'd sooner recommend Imagine). Both single and batch are supported.