How to do it:
1. On Photoshop, open your three different pictures: your elephant, butterfly and background.
2. With your magnetic lasso, go around one wing of the butterfly.
3. Replace the ear of the elephant with the butterfly wing. Erase any ear parts remaining that stick out from behind the wing.
4. Do the same for the next ear.
5. On the side where you have your different layers, right click on the background layer which should be the bottom one and click merge visible.
6. Then once again use your magnetic lasso and go around the elephant and drag him to your selected background tab.
7. Transform him according to your chosen background. (scale, rotate...)