Reader Fred Hendricks wishes to be respectful of others' privacy but isn't quite sure how to go about it. He writes:
I'm working on a just-for-fun movie in iMovie '11 that I'm going to put on YouTube. In one scene you can see a car's license plate in the background. Is there some way I can cover it up?
As long as the camera or car don't move, yes. Like so.
Launch iMovie, select iMovie > Preferences, select the General preference, and enable Show Advanced Tools. Close iMovie's preferences.
Select the clip that shows the license plate so that it's displayed in iMovie's viewer. Press Shift-Command-4 to engage the screen shot selection tool and draw a selection around the license plate. Let go of the mouse or trackpad and a shutter sound will tell you that the screenshot has been saved to the desktop.
Open that screenshot in any image editor that's capable of blurring your image. Do whatever you need to do to make it unreadable and save it to the desktop.
Now drag it over your iMovie clip and in the menu that appears, choose Picture in Picture. The blurred image will appear as a still in iMovie's project pane as well as in the viewer. Adjust the length of the clip so that it covers the license plate for the duration of the clip. Finally, resize the image and place it where you want it.
I mentioned "as long as the camera and car don't move" for a good reason. Picture in Picture (PIP) is great for covering up an unmoving object, but once that object moves, you're in for a world of hurt if you're using iMovie. Yes, you could repeat this trick over and over, adding multiple instances of the image and moving it as the forbidden object shimmies about. But after spending minutes/hours/days/a lifetime doing it, you'll wonder why you didn't just save your money for a more professional video editor that supports keyframe animation. (Final Cut Pro X does, as well as includes a Censor filter made for this sort of thing--though the filter is oval shaped, when what you want is a rectangle.)