Imagemagick makes it really easy to create thumbnails. You just have to use the convert command with the -thumbnail option like this.

convert picture.jpg -thumbnail 120x120 picture-thumbnail.jpg

While that works, it's pretty boring. If you are using a recent version of Imagemagick, they have recently added a -thumbnail option which allows you to create "polaroid-like" thumbnails. These are pretty cool. When you use this command, it adds a thick white border to the picture along with drop shadow. You also get the option of tilting the picture to a jaunty angle. Here's how the command is used.

convert picture.jpg -thumbnail 120x120 -background black -polaroid 10 picture-thumbnail.png

This will result in a black colored drop-shadow and a picture that is angled at 10 degrees. A couple things to note here:

1) Since the resulting picture needs to use transparency (for the drop shadow and the angle), the result needs to be a format (in this case PNG) that supports transparency. JPG does not support transparency.

2) The picture size that is specified (120x120 in this case) is the size of the thumbnail portion of the picture, it does not include the border or shadow.

When you do this, here's what the resulting thumbnails look like.

The result of creating a thumbnail using Imagemagick's -polaroid command.

As with all Imagemagick commands, this one can be run in bulk to make the conversion a fast and easy process.