How to ensure that putting a product's photo in a paper does not violate copyright?
Photography and other creations carry copyright by default

The answer to your part 1 - the exclusive copyright of a photo belongs to someone from the point of its creation, even if no explicit copyright note is attached.

If you had made the photo of that product, then it would be an entirely different question, but redistributing a photo someone else made is legally almost exactly as redistributing a Hollywood movie.

Available for free doesn't imply a permission to redistribute

If something is freely distributed by it's owner, it doesn't come with an implied permission for you to do the same thing. Unless it comes with a licence that explicitly allows you to do so (e.g. the various Creative Commons licences), you don't have a permission to copy that image further. Citing the source doesn't change that.

Lack of response means lack of permission

If you don't have an explicit permission, then you don't have it regardless of reasons - if an author chooses not to communicate with you, then tough luck. It also may be that the company doesn't have free hands in licencing the image - it's quite possible that the copyright is owned by some photographer, and the company has a licence to use it in their website but not in print.

The journal may want clarifications

The journal submission documents will likely include either a statement that all images are your own, or that you have licenced them appropriately. They may leave the licences as your responsibility or require you to send them the documentation.