Facebook has developed a technique to mark images in a data set; so that researchers can determine whether a particular machine learning model has been trained using those images; writes Alexandre Sablayrolles, Matthijs Douze, and Hervé Jégou.

Here is the link: https://ai.facebook.com/blog/using-radioactive-data-to-detect-if-a-data-set-was-used-for-training/