Shortcut:
Use the add image button, you can search all templates for an image, select inside current image, then stretch picture to cover entire frame. Took me a long time to figure this out. Downside, there are different orientations and shapes to some templates, so if you try to cover a horizontal rectangle like Boromir with a square pic it will stretch funny. Just use a base template that matches the pic you are covering it with. Boromir is a horizontal rectangle, Batman and Robin are a square, The Most Interesting Man in the World is a vertical rectangle.