find -type d ( -path ./cache -o -path ./placeholder ) -prune -o  -type f -regextype posix-egrep -iregex '.*.(jpg|gif|tif)$' -exec identify {} ; | awk '{ split($3, wh, /x/); } wh[1] < 500 && wh[2] < 500 { print $1; }'  | while read i; do convert $i -resize 500 -quality 90 $i ; done

find ./ -name "resized*" -exec rm {} ;