Since both of us that answered you are moderators, we may have access while you do not.
I see the below three groups. Of the three, you have one that is under your name and I would expect that you could add the pic to that group and not the others. I will check into this, but in the meantime, would you like me to add the group icon for you? If yes, please let me know which picture and where it is.
Group Maintained by orionpozo
Mystery and Detective readers
Group Maintained by renehasekamp
The Usual Suspects
Group Maintained by ghodur