The second method is for more trickier images to add sky replacements to. For this method we used a colorama effect to turn the setting image into black (where we do not want the sky effect to be) and white (where we do want the sky effect to be). This makes the entire area where we want to apply the sky replacement transparent so the sky fits in perfectly. You can then add effects like a matte choker to make the edges more smooth so everyone will fit perfectly.
This is an example of a sky replacement I created using this method: