No problem. I mentioned this documentation as it was not hinted in your post you were aware and had already begun using UMG.
The only way to render a specific Camera View as an image is to use the Scene Capture 2D actor. This has been improved over the last few iterations of the engine to expose ShowFlags so you can include/exclude certain things the camera renders to the texture.
Scene Capture 2D
The render texture can be directly referenced in UMG as an image which you can resize in your viewport. To save you some performance and a headache, I would pay attention to the auto-activation check box as well as the ‘Capture Every Frame’ option.
Note If you keep all of the show flags activated and the view distance and showflags are all ticked to the max, you will see a drop in performance. This is because you are rendering your entire scene again to a small camera.
Cheers,