ImageMagick usage

add rounded border.sh

# Tweaked http://www.imagemagick.org/Usage/thumbnails/#rounded_border

convert -size 500x500 -alpha transparent xc:none -fill none -stroke black -strokewidth 4 -draw 'roundrectangle 1,1 498,498 12,12' ,border.png
convert -size 500x500 -alpha transparent xc:white -fill black -stroke transparent -strokewidth 4 -draw 'roundrectangle 0,0 499,499 12,12' ,mask.png
convert -background black src.jpg -resize '500^x500^' -gravity center -extent 500x500 -alpha set \
  ,mask.png -compose DstIn -composite \
  ,border.png -compose Over -composite \
  bordered.jpg

make image semi transparent.sh

# https://www.imagemagick.org/Usage/transform/#evaluate

convert rose: -alpha set  -channel A -evaluate divide 2   rose_transparent.png

random mosaic.sh

fs=($(ls [^t]*.jpg | shuf))
convert \( \
           \( tt-${fs[0]} tt-${fs[1]} -append \) \
           \( tt-${fs[2]} tt-${fs[3]} -append \) \
           +append \
        \) \
        t-${fs[4]} \
        \( \
           \( tt-${fs[5]} tt-${fs[6]} -append \) \
           \( tt-${fs[7]} tt-${fs[8]} -append \) \
           +append \
        \) \
        +append \
        ,mosaic.jpg

remove white background.sh

# https://legacy.imagemagick.org/Usage/masking/#bg_remove

convert cyclops.png -bordercolor white -border 1x1 \
          -alpha set -channel RGBA -fuzz 20% \
          -fill none -floodfill +0+0 white \
          -shave 1x1    cyclops_flood_3.png