Protecting yourself from online theft of art work

During a group discussion on Sunday, an artists revealed that she found that some one else had posted a painting done by the artist and was claiming it as her own. The artist is now reluctant to post any more of her art online for fear that her art will be stolen.
I found this data and would like to share it.
https://graphicartistsguild.org/tools_resources/hey-thats-my-work-on-their-web-site

For further information on artist resources of this type, go to:
https://graphicartistsguild.org/tools_resources/browse