Simply, if you provide a thing for free, expect people to take it and use it for free. Artists, writers, programmers, and everyone else included.
If you do not want your “intellectual property” taken and used by others, don’t give it away for free.
Artists are expected to have online portfolio's of their work easily accessible for prospective clients and selection committees for any kind of shows or programs that they apply for. It is considered a mark of professionalism. Jpeg portfolios are too large to send like a resume. The very tool artists use to get work is being used to take work away from them.