It is in the interests of suppliers to give you access to and allow you to use their product images for you web site or other promotions. They will either provide these from their web site images or they will provide you with a media package to download.
There are also product datafeeds available from well established suppliers. These datafeeds can be integrated into certain eCommerce systems and will in many cases contain the images.
As a supplier there should be no watermarks (overlays) promoting their own business. Resellers will rarely use a supplier who insists on promoting their own business using this method.
To copy an image from a web site you can find an option by clicking your right mouse button over the image. Depending on your browser you will find an option which says ‘Save Image As’ or ‘Download Image’. Select this and then choose a location on your computer that you can find later.