Use black and white image as mask?

I’ve created a material, want to use a mask on specular. When I load the black and white image into, either, “weight image” on or specular image, the specularity is the same all over. The image file is a .jpg grayscale 16384x16384. This seems like such a simple task, but I am not able to make this work. Can someone help, please?

@steffen presumably the object already has UV? do you mind taking a screenshot of the texture and the material graph?