#!/bin/zsh

a=`find $1 -type f | grep -E 'gif|jpg'` 
for img in $a  
do 
  echo "found : $img" 
  echo $img | perl -e 'while (<>) { s/(\w+)\.(\w+)$/$1\.thumb\.$2/; print $_ }'\
 | while read thumb 
  do  
    convert -scale 50x50 $img $thumb 
  done 
done