There is a beautiful website where you can browse art and photos that are donated to the public domain. It means that all of the uploaded art may be used in websites, personal profiles, books, prints etc (be sure to check the rights since sometimes there are limited rights).
Many digital artists find their way to this site, I myself have a profile as well with a large collection free art/images to download.

Sometimes I like to browse the platform and see if I can find bdsm related art and on one of these searches I discovered the digital bondage artworks from Esef. In case you prefer a larger format then my gallery provides click the links below the artworks.