Our reply is always, were someone to really want a high resolution image of a piece, they would find a way to get one.
Protecting the images is messy and prevents people sharing legitimately.
Essentially, an artist becomes better known the more their images are shared so we don’t suggest you do anything to stop this.
Were someone to take an image and profit from it, the artist would be covered by copyright laws. The DACS website has a wealth of info on this. http://www.dacs.org.uk/