Add overlays in Earth
Google Earth has a feature called Photo Overlays, which lets you add a levitating photo to any Earth location. Overlays look good, but they're a little tricky to use. They're a good option for more decorative and less functional tours, as although you can use any size of photo, you can't include links and text as you can with placemarkers.
To get round this, you can overlay photos on top of an existing placemarker that includes links and information. To add a photo, load Google Earth, navigate to your photo's location and – this is important – use the middle mouse button to set up a horizontal rather than a top-down view.
Click on 'Add | Photo' in the top menu. If your photo is on your hard disk, use 'Browse' to find it. If it's online, type in the URL in the Link line.
Overlays have some quirks that you need to know about. First, photos are only visible from one side of a given target. You can see the Overlay icon – it looks like a camera – from any side, but the photo is only visible when the viewer is looking at it along the same plane as the image.
The Tilt option angles the photo; use a setting of 90° to give you a ground friendly view floating in space above your location. Second, it's worth keeping in mind that while loading high-res photos online will take a long time, low-res JPEGs will look rough.
Embedding higher quality photos is definitely the way to go. You should also know that your overlay photos aren't visible to other users of Google Earth. To share them you'll have to save your tour into a file that's available for other users to open.
Make a tour
When you've dotted a few photos around Google Earth, you can join them together to create a video fly-through. Creating a photo overlay adds it to Earth's list of locations in the left sidebar.
To record a tour, select 'Add | Tour', hit the 'Record' button and double-click on each location in turn. The view will move between photos, panning in and out automatically to match the default pan, tilt, height (and so on) that you've defined for each photo. You can also click on Paronamio photos to open and close them.
Unfortunately, placemarkers can't be opened to show any photos that you've linked into them. However, if you doubleclick on a placemarker, the view will pan smoothly to a top-down aspect with the placemarker at the centre. You can, of course, move the view manually too.
To add a narration, just plug in a microphone and start talking. Unfortunately, there's no easy to way to save a completed tour as a video file, but if you have screen capture software such as Fraps, or a capture plug-in for your browser, you can grab the sequence indirectly and then add audio and music in a video editor.
Share your tour
To finish things off, save your tour as a file. Right-click on the tour in Earth, and select 'Save Place As…' This creates a KMZ file that you can email to other people or upload to a website. When a Google Earth user double-clicks on this, Earth will load and the tour will start running. A KMZ file is a packaged zip file that includes an editable KML file of XML data.
If you rename the KMZ file and unzip it, you'll be able to open the movement commands for your tour in a text editor and edit the code by hand. The syntax is straightforward enough to make editing very easy, so you can control exactly how your tour moves around the various points of interest.