Using ImageMagick to make thumbs of a folder of images... all this in a shell script for easy batching.

makeThumbs.sh

#!/bin/bash

# modify these two variables to be the width and height of your desired thumbnails
width=250
height=250

clear

echo Resizing your images and making thumbs

for img in `ls *.jpg`
do
    name=${img%.*}
    ext=${img#*.}
    convert -sample ${width}x${height}^ -gravity center -crop ${width}x${height}+0+0 $img $name-thumb.$ext
done