Add text watermark with imagemagic (example)

watermark.sh

#!/bin/bash

mkdir img-with-watermark
WATERMARK='Some text here'

for FILE in *.jpg; do
    W=`identify -verbose "$FILE" | grep -oe "Geometry:.*" | sed -e 's/.*: //' | sed -e 's/x.*//'`
    H=`identify -verbose "$FILE" | grep -oe "Geometry:.*" | sed -e 's/.*x//' | sed -e 's/+.*//'`
    convert -background '#0000' -fill '#0004' -gravity center -size "$W"x"$(($H / 6))" caption:"$WATERMARK" ./"$FILE" +swap -gravity center -composite ./img-with-watermark/"$FILE"
done