1. Install GraphicsMagick
On Ubuntu (14.04):
sudo apt-get install graphicsmagick
2. Install the Node library in your project
npm install gm
3. Write a script
Below I show two ways of creating a thumbnail. The first way creates a JPG using various GraphicsMagick functions, I prefer this way because it gives me fine grained control over the thumbnail. The second uses a built in function for thumbnails, which is easy to use but isn’t as flexible.