Try to change to fix class not found.

plugin.xml

@@ -15,7 +15,7 @@
     <platform name="android">
         <config-file target="res/xml/config.xml" parent="/*">
             <feature name="CustomCamera">
-                <param name="android-package" value="org.geneanet.customCamera"/>
+                <param name="android-package" value="org.geneanet.customCamera.CameraLauncher"/>
             </feature>
         </config-file>
         <config-file target="AndroidManifest.xml" parent="/*">

www/customCamera.js

@@ -16,7 +16,7 @@ customCameraExport.prototype.getPicture = function() {
 };
 
 customCameraExport.prototype.startCamera = function() {
-    cordova.exec(
+    exec(
         function(result) {
             console.log("success");
             console.log(result);