Well, my topic title is pretty descriptive. Does GD use much server ressources, is it heavy to run, or is it light and flawless just like a normal PHP script? If I use GD much, should the images be cached?

And by the way, I don't know how to cache images. I know how to create them, but I can't manage to store them in a folder, and then check that folder to see if the file is already cached. If it's not, the PHP script will create it.