I quite often just drag and drop my important files onto a blank cd to back them up this has worked for me for quite some time. It will be the same with an external hard drive if you ever need them you can just open the files up on your hard drive and copy them back.
The advantage of using a dedicated backup program is that you can set it to do incremental backups at set times.
Also when you say images files are you talking about an image created by a program like ghost or acronis true image? Thats the way most people backup now because it creates a complete image of your hard drive and you can restore from it in about 10mins and be back to the day you made the image. Image programs such as that support incremental backups as well.