What is the difference between analog surveillance cameras and HD surveillance cameras?

It all comes down to Quality. If there is a break-in, you are much more likely to have a suspect identified or get a license plate number if you have HD surveillance cameras. Analog cameras only provide a standard, non-HD picture. Whereas HD cameras provide a crystal clear up to 5MP picture. The price difference is significant. You will pay quite a bit more to have that quality at your fingertips. I recommend a "Hybrid" system of some sort. This will allow you to use a mixture of analog and HD cameras.