Inside the booth
Create background separation when the booth must sit near a wall
Use angle, light and a simple crop to prevent a flat shadow behind the subject.
A small room may leave little space between person and wall. You can still separate the face from the background by changing the camera angle, turning the subject and avoiding a bright light aimed straight at the wall.
Angle the subject
Move the person a little away from the wall if possible and turn their shoulders slightly. Keep the face toward the camera. Even a small diagonal can separate the hair and shoulder outline from the backdrop.
Move the light
Place a continuous light to one side of the camera rather than directly above the lens. Watch the wall for a sharp head shadow and shift the light farther sideways until the shadow moves outside the crop.
Test the edges
Take a frame and check the shoulders, hair and wall shadow. If the outline still merges, use a darker or lighter background with better contrast, or crop tighter without cutting the head. Do not increase background blur digitally until edge halos appear.