An overlay is an image added on the top of Google Earth

There are three types of Overlays

Ground Overlays

Screen Overlays

Photo Overlays

What is a Ground Overlay?

A ground overlay is also known as Image Overlay

Is an image draped onto the terrain of the Google Earth

Or an image added to Google Earth at a specified altitude

It follows the curvature of the Earth

Supported file formats: BMP, DDS, GIF, JPG, PGM, PNG, PPM, TGA, TIFF

Syntax

<GroundOverlay id="ID">
  <altitude>0</altitude>                  
  <altitudeMode>clampToGround</altitudeMode>
  <LatLonBox>
    <north>...</north>                     
    <south>...</south>                     
    <east>...</east>                      
    <west>...</west>                      
    <rotation>0</rotation>               
  </LatLonBox>
</GroundOverlay>

Example

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2">
    <GroundOverlay>   
    <name>GroundOverlay.kml</name>
        <color>fff000022</color>   
        <drawOrder>1</drawOrder>   
	<Icon>      
	   <href>http://vislab.eas.ualberta.ca/VisLab/images/techniques/graph02.png</href> 
	</Icon>   
	<LatLonBox>      
	    <north>53.53234</north>      
	    <south>53.532122</south>      
	    <east>-113.513033</east>      
	    <west>-113.513724</west>      
	    <rotation>45</rotation>   
	</LatLonBox>
   </GroundOverlay>
</kml>

Result

What is a Screen Overlay?

A screen overlay is an image drawn on the screen instead of Google Earth

Location and size are fixed

show Logo or legends

Screen and Overlay Coordinates

Syntax

<ScreenOverlay id="ID">
    <Icon>
    <href>...</href>
    </Icon>
    <overlayXY x="..." y="..." xunits="fraction" yunits="fraction"/>    
    <screenXY x="..." y="..." xunits="fraction" yunits="fraction"/>      
    <rotationXY x="..." y="..." xunits="fraction" yunits"fraction"/>  
    <size x="..." y="..." xunits="fraction" yunits="fraction"/>              
    <rotation>...</rotation>                  
</ScreenOverlay>

Example

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2">
<Document>
   <ScreenOverlay>   
        <name>Rotate 45</name>
	<Icon>      
	   <href>http://vislab.eas.ualberta.ca/vislab/images/sdv_logo.png</href> 
	</Icon>   
	<overlayXY x="0.05" y="0.95" xunits="fraction" yunits="fraction"/>
        <screenXY x="0.05"  y="0.65" xunits="fraction" yunits="fraction"/>
	<size x="0" y="0" xunits="fraction" yunits="fraction"/>
        <rotation>45</rotation>
    </ScreenOverlay>
   <ScreenOverlay>   
        <name>Rotate -45</name>
	<Icon>      
	   <href>http://vislab.eas.ualberta.ca/vislab/images/sdv_logo.png</href> 
	</Icon>   
	<overlayXY x="0.05" y="0.95" xunits="fraction" yunits="fraction"/>
        <screenXY x="0.05"  y="0.35" xunits="fraction" yunits="fraction"/>
	<size x="0" y="0" xunits="fraction" yunits="fraction"/>
        <rotation>-45</rotation>
    </ScreenOverlay>
   <ScreenOverlay>   
        <name>Rotate 0</name>
	<Icon>      
	   <href>http://vislab.eas.ualberta.ca/vislab/images/sdv_logo.png</href> 
	</Icon>   
	<overlayXY x="0" y="0" xunits="pixels" yunits="pixels"/>
        <screenXY x="10"  y="560" xunits="pixels" yunits="pixels"/>
	<size x="0" y="0" xunits="fraction" yunits="fraction"/>
        <rotation>0</rotation>
    </ScreenOverlay>
  </Document>
</kml>

Result

What is a Photo Overlay?

A Photo overlay is an image placed at a given location of Google Earth

It is oriented toward the view point

It can have one of the three shapes: rectangel, cylinder, sphere

Camera

<Camera id="ID"> <longitude>0</longitude> <latitude>0</latitude> <altitude>0</altitude> <heading>0</heading> <tilt>0</tilt> <roll>0</roll> <altitudeMode>...</altitudeMode> </Camera>

ViewVolume

<ViewVolume> <near>1000</near> <leftFov>-60</leftFov> <rightFov>60</rightFov> <bottomFov>-45</bottomFov> <topFov>45</topFov> </ViewVolume>

Adding Very Large Photo

Check here