What are you trying to achieve is definitely feasible. You are trying to do that via System built-in functionality. Issue here is that user is expected to take picture and confirm that it is valid. Than, result (image URL) is brought back to your activity. So, it is not robotium.
Another approach is to use fact that Android offers you complete control over Camera via
android.hardware.Camera;
It is definitely more demanding approach. But if you use existing example from your Android installation as guideline
android-sdk-windows\samples\android-8\ApiDemos\src\com\example\android\apis\graphics\CameraPreview.java
it should be achievable. Do not forget to declare permissions in your manifest, as descibed in the Camera
SDK documentation.