Zen Cart does not link to product images from an external site, for two main reasons:
- other sites don't usually like you using 'their' bandwidth to display images on 'your' site ... esp since images are the largest traffic component on most sites.
- personal firewall software such as zonealarm and norton internet security, adaware, etc, typically block images that come from other websites, because that is the typical method by which banner ads are displayed. FireFox sometimes will even do this by default depending on its ad-blocker settings.
You'd be better off getting the images from your supplier on a periodic basis, or perhaps buy a program that will steal all the content+images from another (their) site, and use that to grab your supplier's images for your use ... assuming of course you are allowed to do that in your contracts with them. Then upload the desired images to your site as part of your product details.