There are two things you can do first: send a polite email to the companies, stating you are the author of the image that they purchased and you are grateful that they chose your image but you kindly ask them to remove the high res image or include visible watermarks (i.e. transparent version of their logo) so they cannot be copied. This not only protects you but their investment as well. Since they paid for the image it makes no sense to allow other people to use it.
Another thing is to email Google and ask them to stop distributing high-res copyrighted images. As weird as this may sound, it's much probable that the high res image that you noticed were downloaded via Google Images rather than from a competitor's website.
You can contact them using the two links provided in this blog article
If you want to go more than that, you can remove your high res (unwatermaked) images following these instructions
300v (film), assorted lenses ...