Takes all jpgs from the source folder and copies only the jpgs that present a significant difference, used to remove repeated frames from webcams output.

movement.sh

#/bin/bash
#We only allow empty destination folders.
if [ -d "$2" ]; then
  echo "Directory already exists"
	exit
fi
#If it doesn't exists create it.
if [ ! -d "$2" ]; then
  mkdir $2
fi
directory="$2/"
#You can change this to react to smaller changes, but i have found this number to be very good.
threshold=5000
images=($(ls -1 $1/*.jpg))
i=1
last_image=${images[0]}
images_count=${#images[@]}
diffe=0
percent=0
while [ $i -lt $images_count ]
do
	#We use compare from imagemagick with a little fuzz, 10% on fuzz and 5000 on threshold seems to work very good.
	diffe=$(compare -metric AE -fuzz 10% $last_image ${images[i]} null: 2>&1)
	percent=$(echo "scale=2; $i*100/$images_count" | bc)
	echo  "$i/$images_count($percent%)"
	#We only process images that are significally different from the previous one.
	if [ "$diffe" -gt "$threshold" ]; then
		echo ${images[i]}
		echo $diffe
		#We use the last processed image as the comparition point
		last_image=${images[i]}
		cp $last_image $2
	fi
    	(( i++ ))
done

Usage:
./movement.sh source destination

Created using examples from ImageMagick documentation here: http://www.imagemagick.org/Usage/compare/