Those instructions are very old and not intended for a single image.
In your case you need to give your still image some "time" (duration). Easy to do with QuickTime Player Pro.
Open any audio file in QuickTime, make a selection (in and out points) that matches the duration you wish for the image file. Let's say an mp3 with a ten second selection. Leave this window open.
Open your image file in QuickTime. Select All (Edit menu) and Copy. Close this window.
Switch to your audio file selection. From the Edit menu choose Add to Selection & Scale. You'll see the window expand in dimensions as your image is added.
Open the Movie Properties window (Windows menu). You'll notice it now has a "Video" track.
Single click on the Video track and then click the "Extract" button (upper left of the window). The ten second video track will open in a new Player window.
Close the audio file window without saving.
Do a "Save As" on the image video track. Give this new .mov file a name and location. Leave the window open.
Select All and copy the ten second video track. Switch to the movie file you want to add it to and move the playhead to the end. From the Edit menu "Paste" the ten second video. It will be added to the end of the movie.
Save As (self contained) and name the new video.