Ubercart Marketplace - Where is the ImageField for users?
It sounds like you need to check the permissions (/admin/user/permissions).

If you have field level permissions then you'll want to look for your CCK imagefield for your product images under the heading "content_permissions module." Ensure that the "view field_YOURIMAGEFIELD" permission is checked for all users.

Also if you're using imagecache on your product images there is also a permission for that as well.

Just for general knowledge the super admin user (user 1) completely bypasses the site permissions even if the super admin is assigned a role. It's a good idea to create a new user and create a new role to assign it to. Then use this user instead of 'admin.' We create a role called 'Site Architect.'

Hope that helps!