Add a camera to your scene.
Keep your live action background plate as a 2D group.
Add a Grid and make the BG Opacity zero.
Adjust your camera so the grid lines up with the perspective lines of your car number plate.
At that point when you add in your new number plate – also in a 3D group it will be easy to line it up pretty much perfectly.
It stop position has an X rotation of about 14-15 degrees so you’ll need to work with that.
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