I just gave a powerpoint presentation hooking my macbook up to a projector. I was in "presentation mode" I think it's called- where I can see my computer functioning normally and can see powerpoint's 'presenter tools' but all that's being displayed on the projector is the powerpoint itself. (excuse me, i'm clearly not very literate in these things) Anyway, when I turned my computer on, before I got powerpoint open, (when the projector was supposed to just be displaying my desktop image) the projector was displaying this image that was my desktop image a couple of days ago. Then, when I had to restart my computer, it started displaying another random picture from my hard drive. Luckily it wasn't anything embarrassing, but how do I keep this from happening in the future? How do i control which image comes up as my background image? Thank you so much!