Why can my friends see my pictures?

[Lorely]

Hi i posted a picture on an event on facebook, but i don't want my whole entire friendlist to see it!
I went through my wall but i just can't figure out how they can see it. It's not on my wall! I even went to the privacy settings and looked at my profile as one of my friends, but i still can't see the picture on my wall. So how do they see it? and how can i do so that they can't see it. When i look at my "activity" and look the picture it says "public" but i can't change it. The only option i have is to delete it. Any way i can do so my friends can't see it anymore?