Wherever you "purchase high resolution artwork", be sure to check the Seller's terms and conditions for use of the artwork. Some Sellers' terms and conditions for using their art they created may restrict the artwork to one-time and private or non-commercial use only.
Shutterstock claims to be a free online service, lists and categorizes the pics they find online claiming the pics are in the public domain on the Internet, but the pics may still be copyrighted and owned by an undisclosed or unknown 3rd party person or company. The devil is in the details.
If the Owner of copyrighted artwork does not want the artwork distributed or made available on the Shutterstock website, they can send a "cease and desist" letter to Shutterstock to remove the artwork from Shutterstock and get a list of login names or IP addresses that downloaded the artwork.
However, a high-resolution pic about "teak wood for a boat transom" would be hard to trace as copyrighted artwork listed by Shutterstock or another online vendor because it would be difficult to prove as a unique work of art unless it is copyrighted.