[someone@someones-pc ~]$ for i in *.mp4; do ffmpeg -i "$i" -i watermark.png -filter_complex "overlay=1623:25" /output/directory/"${i%.*}.mp4"; done

#!/bin/bash

WM=$HOME/public_html/image/catalog/logo-website/watermark.png  # This is the path to your watermark image
SCALE=100                          # This sets the scale % of your watermark image
STARTDIR="/home/whatever/images"   # This is the directory to start in

for imagedir in $( find $STARTDIR -type d )
do
  echo "Running in $imagedir ..."
  cd $imagedir
  file -i * | grep image | awk -F':' '{ print $1 }' | while read IMAGE
  do
    echo "Watermarking $IMAGE"
    composite -dissolve 40% -gravity SouthEast -quality 100 ( $WM -resize $SCALE% ) "$IMAGE" "$IMAGE"
  done
done