[support] Only images hosted on this site may be used in <img> tags

I was answering a question on a LinkedIn group and went to D.O to check the Input format description. At the bottom, it says "Only images hosted on this site may be used in <img> tags. Others are replaced with an error icon." Does anyone know if that filter code is available, preferably as a contrib?   Nancy  Injustice anywhere is a threat to justice everywhere. -- Dr. Martin L. King, Jr.