Macbook Pro changing desktop picture randomly I just got back from vacation and while on vacation I turned my computer off for the 5 days I was gone. I just now turned it back on and my desktop picture was changed to the galaxy photo which I know I didn't do because it was a picture of my dog when I left. It was locked in my basement so I know that no one could be messing with me. I also have noticed that my computer is running a little slow, but I don't know if that has anything to do with it? Also I know there is a setting that you can choose to have it change your picture every 30 min. or so, but I checked and that wasn't the problem for desktop 1 or desktop 2.

How can I prevent this happening in the future? Or this an indication of a "deeper" problem?
We have seen this on occasion.  Our solution has been to:


go to Desktop &amp; ScreenSaver (Apple>System Preferences) 
Choose a different photo (or folder)
Change the "CHange Picture" time to something different.
CHange back both ("change picture" time and photo) to original settings.
close Preferences tab..


The theory we hold is that the preferences are sometimes getting corrupted, and over-writing/re-writing is fixing it....