Stan, I'm afraid just adding a comment won't stop it.
Instagram allows you to filter comments by keywords (which you can also define to your personal taste like... hm... "posting", "my" and "photos")
Such filtered comments are then hidden from the public eye.
Reporting a copyright infringement to Instagram isn't easy either. In the contact sheet you have to give your full name, home address, telephone number and email address. What bothers me is that they furthermore say:
"Please be aware, that on a regular basis we are giving your contact information to the person who uploaded the content you are reporting, including name and email address (...) and/or the content of your report."
I really don't know why the person I am reporting should have this data when I have nothing more than a user name...