Maybe the same thing as Imagemagick's "bg_removal.sh"

bg_remove.sh

#!/bin/zsh

# an image that looks like the background
WHITE=/Users/andre/Desktop/white.png

# output directory
OUT=/Users/andre/Pictures/mugshots_no_bg

# maybe run us like this:
# find ... -name '*.jpg' | xargs -n 100 -P 4 -J % ~/bin/bg_remove.sh %

for img in $@; do
    file=$(basename "${img}")
    filename=${file%.*}
    filedir=${img:a:h}
    pngfile="${filename}.png"
    pngpath="${filedir}/${pngfile}"
    # Combination of flood-fill and difference mask methods (see below)
    magick convert "${img}" "${WHITE}" \
            \( -clone 0 -clone 1 -compose Difference -composite \
            -fill white -fuzz "10%" +opaque black -fuzz "20%" -blur "0x2" \) \
        -delete 1 -alpha off -compose copy_opacity \
        -composite "${OUT}/${pngfile}" 
done

# https://legacy.imagemagick.org/Usage/masking/#bg_remove
#
# Just a format conversion:
# magick "${img}" "${pngpath}"
#
# Naive flood-fill method that changes the color at position 0,0 
# to transparent; no structural awareness, can have holes
#
# magick convert "${pngpath}" "-fuzz" "20%" "-fill" "magenta" \
# "-draw" "color 0,0 floodfill" "-transparent" "magenta" "${pngpath}"
#
# Difference mask method is given an image of the background, but has the 
# same drawbacks as the flood-fill method.
#
# magick convert "${filedir}/white.png" "${pngpath}" "-fuzz" "30%" \
# "${filedir}/white.png" -compose ChangeMask  -composite  "${pngpath}"