There are a number of apps on the market that will backup for you. On a mac it comes with Time machine.backs up automatically. There are also apps that come with external hard drives, Lacie supply one for Mac and PC with each of there drives, but it will only back up to LaCie drives
Widows 7 I believe has a back up facility as well ( wouldn't know too much about that as I'm on Macs)
Theses apps simply copy the files from the source drive to the back up drive. They are not normally compressed ot encrypted, unless you ask the software to do it. Simply opening the folder on the back up drives revels the files as normal.
The easiest way to manually back up is to store your images within a single folder ( You can have sub folders within this to help searching ) and then on a regular basis just copy this top level folder to your back up drive. OK you copy images you have already saved, but this makes sure you don't forget anything