I'm developing an iOS geospatial application that can export to KMZ. Geotagged photos are bundled along side the KML into a zipped KMZ. Here is a snipped of the placemarks description tag:
<![CDATA[ <img src="myphoto.png" /> ]]>
When loading the KMZ into the online Google Earth it shows as a failed image but it does work on the Google Earth Pro desktop viewer.
I've been through the docs and tried different flavours of local references but nothing has worked. Frustratingly, the documentation for KMZ has this sample file which also doesn't work in the web viewer.