a group is using a picture of me and slandering me without my permission and refuse to take it down
If the group is making false and defamatory
written or pictorial statements about you, that would be considered libel instead of slander. Slander is the oral or spoken form of defamation.
For advice on what to do about this group that is causing you trouble, and for possible ways you can get the picture of you and the defamatory material written about you removed from its online location, you will need to provide more details, starting with the name of your state (if you are in the US) or the name of your country (if you reside outside the US).