title: Android take photo on unlock secretly
body: <p>I am trying to build an app which captures a photo everytime the phone is unlocked. The user should not see that a photo has been taken. So it should basically behave like an anti-theft app.</p>
  
  <p>I have read that I should use a dummy SurfaceTexture, so the preview is not shown on the screen, but I am not able to capture a photo.</p>
  
  <p>Here is what I have written so far. It is just a sample activity to get in touch with the Camera object:</p>
  
  <pre><code>package com.brushmate.chameleon;
  
  import java.io.IOException;
  
  import android.graphics.SurfaceTexture;
  import android.hardware.Camera;
  import android.os.Bundle;
  import android.os.SystemClock;
  import android.annotation.SuppressLint;
  import android.app.Activity;
  import android.util.Log;
  import android.view.SurfaceView;
  
  public class SettingsActivity extends Activity {
      private static final String TAG = "Chameleon Wallpaper";
  
      @SuppressLint("NewApi") protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_settings);
  
          Log.d(TAG, "Activity created");
  
          Camera cam = getCamera();
  
          if (cam != null) {
              Log.d(TAG, "Camera available");
  
              SurfaceTexture dummy = new SurfaceTexture(0);
  
              try {
              cam.setPreviewTexture(dummy);
              } catch (IOException e) {
                  // TODO Auto-generated catch block
                  e.printStackTrace();
              }
  
              Log.d(TAG, "Preview texture set");
  
              cam.startPreview();
  
              Log.d(TAG, "Preview started");
  
              cam.takePicture(null, null, new Camera.PictureCallback() {
  
                  @Override
                  public void onPictureTaken(byte[] data, Camera camera) {
                      Log.d(TAG, "Image taken");
                  }
              });
  
              cam.stopPreview();
  
              Log.d(TAG, "Preview stopped");
  
              cam.release();
  
              Log.d(TAG, "Camera released");
          }
      }
  
      private Camera getCamera() {
          Camera cam = null;
  
          try {
              cam = Camera.open();
          } catch (RuntimeException e) {
              Log.e(TAG, "Camera not available", e);
          }
  
          return cam;
      }
  
  }
  </code></pre>
  
  <p>And here is my Logcat output:</p>
  
  <pre><code>05-12 23:54:56.947: D/Chameleon Wallpaper(19614): Activity created
  05-12 23:54:56.947: I/AwesomePlayer(161): setDataSource_l(URL suppressed)
  05-12 23:54:56.977: I/AwesomePlayer(161): setDataSource_l(URL suppressed)
  05-12 23:54:57.007: I/CameraClient(161): Opening camera 0
  05-12 23:54:57.117: E/mm-camera(175): sensor_load_chromatix: libchromatix_imx111_preview.so: 30
  05-12 23:54:57.217: E/mm-camera(175): vfe_ops_init: E
  05-12 23:54:57.237: E/mm-camera(175): vfe_legacy_stats_buffer_init: AEC_STATS_BUFNUM
  05-12 23:54:57.237: E/mm-camera(175): vfe_legacy_stats_buffer_init: AEC_STATS_BUFNUM
  05-12 23:54:57.247: E/mm-camera(175): mctl_init_stats_proc_info: snap_max_line_cnt =30096
  05-12 23:54:57.267: D/Chameleon Wallpaper(19614): Camera available
  05-12 23:54:57.267: D/Chameleon Wallpaper(19614): Preview texture set
  05-12 23:54:57.267: E/QCameraHWI(161): android::status_t android::QCameraHardwareInterface::setPreviewWindow(preview_stream_ops_t*): mPreviewWindow = 0x0x400b9e98, mStreamDisplay = 0x0x4008c378
  05-12 23:54:57.267: D/QCameraHWI(161): android::status_t android::QCameraHardwareInterface::startPreview():  start preview now
  05-12 23:54:57.267: I/QCameraHWI(161): android::status_t android::QCameraHardwareInterface::startPreview2():Setting ZSL mode
  05-12 23:54:57.267: E/mm-camera(175): config_proc_CAMERA_SET_INFORM_STARTPREVIEW
  05-12 23:54:57.267: E/mm-camera(175): config_update_stream_info Storing stream parameters for video inst 1 as : width = 640, height 480, format = 1 inst_handle = 810081 cid = 0
  05-12 23:54:57.307: E/mm-camera(175): config_update_stream_info Storing stream parameters for video inst 3 as : width = 640, height 480, format = 1 inst_handle = 830083 cid = 0
  05-12 23:54:57.307: E/mm-camera(175): config_update_stream_info Storing stream parameters for video inst 4 as : width = 512, height 384, format = 1 inst_handle = 840084 cid = 0
  05-12 23:54:57.307: E/mm-camera(175): config_decide_vfe_outputs: Ports Used 3, Op mode 1
  05-12 23:54:57.307: E/mm-camera(175): config_decide_vfe_outputs Current mode 0 Full size streaming : Disabled
  05-12 23:54:57.307: E/mm-camera(175): config_decide_vfe_outputs: Primary: 640x480, extra_pad: 0x0, Fmt: 1, Type: 1, Path: 1
  05-12 23:54:57.307: E/mm-camera(175): config_decide_vfe_outputs: Secondary: 640x480, extra_pad: 0x0, Fmt: 1, Type: 3, Path: 4
  05-12 23:54:57.307: E/mm-camera(175): config_update_inst_handles Updated the inst handles as 810081, 830083, 0, 0 
  05-12 23:54:57.387: W/ActivityManager(592): Activity pause timeout for ActivityRecord{420bd848 u0 com.brushmate.chameleon/.SettingsActivity}
  05-12 23:54:57.447: E/mm-camera(175): sensor_load_chromatix: libchromatix_imx111_zsl.so: 26
  05-12 23:54:57.537: E/mm-camera(175): camif_client_set_params: camif has associated with obj mask 0x1
  05-12 23:54:57.537: E/mm-camera(175): config_v2_CAMERA_START_common CAMIF_PARAMS_ADD_OBJ_ID failed -1 
  05-12 23:54:57.537: E/mm-camera(175): vfe_operation_config: format 3
  05-12 23:54:57.537: E/mm-camera(175): vfe_operation_config:vfe_op_mode=5
  05-12 23:54:57.537: E/mm-camera(175): Invalid ASD Set Params Type
  05-12 23:54:57.537: E/mm-camera(175): vfe_set_bestshot: Bestshot mode not changed
  05-12 23:54:57.567: D/Chameleon Wallpaper(19614): Preview started
  05-12 23:54:57.607: E/mm-libcamera2(161): PROFILE HAL: First preview frame received: 1368395697.614272749
  05-12 23:54:57.607: E/BufferQueue(19614): [unnamed-19614-0] dequeueBuffer: min undequeued buffer count (2) exceeded (dequeued=6 undequeudCount=0)
  05-12 23:54:57.647: E/mm-libcamera2(161): mm_camera_dispatch_buffered_frames: mframe 0x0, sframe = 0x0
  05-12 23:54:57.647: E/mm-libcamera2(161): PROFILE HAL: stopPreview(): E: 1368395697.653949232
  05-12 23:54:57.647: E/mm-camera(175): config_MSG_ID_STOP_ACK: streamon_mask is not clear. Should not call PP_Release_HW
  05-12 23:54:57.667: D/Chameleon Wallpaper(19614): Preview stopped
  05-12 23:54:57.667: E/mm-libcamera2(161): PROFILE HAL: stopPreview(): E: 1368395697.676839512
  05-12 23:54:57.667: E/QCameraHWI(161): android::status_t android::QCameraHardwareInterface::setPreviewWindow(preview_stream_ops_t*):Received Setting NULL preview window
  05-12 23:54:57.677: E/QCameraHWI(161): android::status_t android::QCameraHardwareInterface::setPreviewWindow(preview_stream_ops_t*): mPreviewWindow = 0x0x0, mStreamDisplay = 0x0x4008c378
  05-12 23:54:57.677: W/QCameraHWI_Preview(161):  Setting NULL preview window 
  05-12 23:54:57.677: I/CameraClient(161): Destroying camera 0
  05-12 23:54:57.687: E/mm-camera(175): config_shutdown_pp Camera not in streaming mode. Returning. 
  05-12 23:54:57.687: E/mm-camera(175): vfe_ops_deinit: E
  05-12 23:54:57.758: D/Chameleon Wallpaper(19614): Camera released
  05-12 23:54:57.758: W/AudioFlinger(161): session id 77 not found for pid 161
  05-12 23:54:57.758: W/AudioFlinger(161): session id 78 not found for pid 161
  05-12 23:54:57.808: D/libEGL(19614): loaded /system/lib/egl/libEGL_adreno200.so
  05-12 23:54:57.808: D/libEGL(19614): loaded /system/lib/egl/libGLESv1_CM_adreno200.so
  05-12 23:54:57.808: D/libEGL(19614): loaded /system/lib/egl/libGLESv2_adreno200.so
  05-12 23:54:57.818: I/Adreno200-EGL(19614): &lt;eglInitialize:269&gt;: EGL 1.4 QUALCOMM build: Nondeterministic AU_full_mako_PARTNER-ANDROID/JB-MR1-DEV_CL2961380_release_AU (CL2961380)
  05-12 23:54:57.818: I/Adreno200-EGL(19614): Build Date: 12/10/12 Mon
  05-12 23:54:57.818: I/Adreno200-EGL(19614): Local Branch: 
  05-12 23:54:57.818: I/Adreno200-EGL(19614): Remote Branch: m/partner-android/jb-mr1-dev
  05-12 23:54:57.818: I/Adreno200-EGL(19614): Local Patches: NONE
  05-12 23:54:57.818: I/Adreno200-EGL(19614): Reconstruct Branch: NOTHING
  05-12 23:54:57.848: D/OpenGLRenderer(19614): Enabling debug mode 0
  05-12 23:54:57.888: I/ActivityManager(592): Displayed com.brushmate.chameleon/.SettingsActivity: +1s63ms
  </code></pre>
  
  <p>As far as I understood, the procedure is correct. So what am I doing wrong?</p>