Clonezilla all the way for me. You'll need enough space on a disk (external USB, I guess) to clone the whole image on, which might be your problem. A disk with 100 GB usage will create you an image of around 50-80 GB, so be aware of this. After all, the "save to disk" option from Clonezilla isn't their main usage, as the tool is coming from school use where they set up whole classrooms of PCs directly from a central server. It works for single clone copies as well, but it's much more powerfull than "just" make a security copy of your disk.