When you start an ecommerce site selling CDs and books

How do you get the rights to use the images?

[TomWaits]

If you're an affiliate somewhere, do they just point you somewhere to download all the images?

If you start a site from scratch, without being an affiliate of anybody, how do you get those images?

[Kevin French]

Tom:

Several vendors supply datafeeds that will include urls of the of the corresponding products along with other relevant info.

Check with the merchant to see if that is an option for you.