There weren't many decent captures of Kennedy Lake in my collection, so this one had to be fixed: It's easy enough to create a new layer from the background, so that another layer can be placed behind it; And it's easy to select the blown-out sky, but then I use the "grow" command, and after that expand the selection by a pixel or two before cutting it out. It's more tricky to get the color balance right when pasting in a sky from a different shot. Since the Sun angle is low, this sky needed more red and less blue. I'm not sure I got it right. But then comes the key: Select the entire background layer with the magic wand set to maximum (255), so that it finds the edge of the cutout. Then select > modify > border, around three pixels wide, to select just the ragged edge of the skyline. Then very slightly blur the border selection before flattening the whole image. No more cutout artifact! Voila - Not a masterpiece, but presentable. Total time around five minutes.