Superimpose:
1. Open your photo then your sash move it where you want and merge and save

Picsart:
1. open your photo in picsart then go to draw and open your sash and turn your so it looks like this. It makes it easier to erase the back ground.

2. Then put it on erase and make the shape a square and erase the back ground like so.

3. Go to transform and move your sash to were you want it then hit the check mark and save.