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when I attempted to save the picture to my desktop I got an error message that said I couldn't save the picture because I didn't have permission put it in that folder. At that point I couldn't figure out why I couldn't put it on the regular desktop. I finally found that the desktop folder it was attempting to use was my user folder. Why, I have no idea.
Just trying to "read between the lines" here and not implying that you did anything wrong. If you have more than one account, it is not that hard to 'wander' into another "user" account and even their 'Desktop.' I'd simply suggest that, in any "Find/Save/Save as.." dialog, you use the command-d keyboard shortcut to be sure that you are selecting your own Desktop. Of course, making sure different users have distinctly different names will also help.
All that said, I think
Kriss's instruction will solve your immediate problem.