Note

Invert: shift + ctrl + I

To get an object to a different image:
- need a selection !
- copy and paste
- drag and move it

Drop shadow:
- make a duplicate layer of the object
- If you only want the chosen image and NOT the background, choose Transparency lock.
- Fill with black
- Filter > Gaussian Blur

To get a selection back, hold ctrl key and click on the thumbnail.