I don’t think you can just per sé. The clickable area of a button is defined by the dimensions in the WidgetBlueprint and not by the transparency of a button’s image. So what you can do is create an extra Image under your button. If you then make the button texture fully transparent, and the scaling of the button quite small, you should get the desired effect. Yet, as far as I know, there is no thing as button masking. But i could be wrong here.