Geodatabase attachments are not exported to the KMZ. In order to view the image, you'd need to save the photo to a location that is web enabled and add they hyperlink of the image to a field in your feature class. Then you would need to modify the html popup xsl template in the layer properties to include a test for field values.
<xsl:when test="FieldValue[starts-with(., 'http://yourimageserver.com/image_directory/')]">
<a target="_blank">
<xsl:attribute name="href"><xsl:value-of select="FieldValue"/>
</xsl:attribute>
<img>
<xsl:attribute name="src">
<xsl:value-of select="FieldValue"/>
</xsl:attribute>
<xsl:attribute name="width">
<xsl:value-of select="250"/>
</xsl:attribute>
</img>
</a>
</xsl:when>
The photo will show up in the html popup in ArcMap in the table provided the url base included in the XML test matches the beginning of the URLs for the photos. When exported to KMZ, the html popup should look the same in google earth. It will also hyperlink to the photo for full screen viewing.