This tutorial can be made with all versions of PI, I used PI XL.
Skill level: beginner
No outside filters are used.
We start with a photo like this and duplicate it.
Crop the photo like this.
Frame the image with 1p black 10p white and 1p black.
From the original photo select the front part of the dolphin and make it an object and erase the background.
Place it then on the image and try to make it "seamless". Merge as single object.
Open a canvas bigger than your image and fill with color or some texture. Place your image on the canvas and you are ready.
It was easy, wasn't it.