@Shizai Basically when you do a widget image, and you set the correct resolution of the image in the detail panel you should then add that widget to a Blueprint actor:
This was the only way I could get UE to render the image properly without losing quality is by increasing the draw size to the correct resolution or duplicating it which adds more fidelity if I’m not mistaken.
Try it yourself, because the image size option in the widget itself is just defining the image scale but not resolution where as the one in the blueprint actor is more of a resolution definition rather than physical scale.