Cloning is about making a copy of your HDD before replacing it with another drive and copying back. (sorry to be pedantic)
What I think you want is a disc "image" which is a copy of everything including your operating system so you can restore data if it is lost or corrupted.
You do not need an external HDD to image but obviously it cannot protect you from a HDD failure if your image is also on it. Whilst you can copy an image to several DVDs or the like the most straightforward way is to copy to an external HDD. You can of course copy just the pictures ot other files to the same HDD as well as the image if you wish.