how to take camera capture without a preview from a service or thread?

Try this code. It will click a picture when the activity starts up. It has a preview, but the preview size is set to 0 by 0 dp.

package fortyonepost.com.pwop;

import java.io.IOException;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.hardware.Camera;
import android.hardware.Camera.Parameters;
import android.os.Bundle;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.ImageView;

public class TakePicture extends Activity implements SurfaceHolder.Callback
{
    //a variable to store a reference to the Image View at the main.xml file
    private ImageView iv_image;
    //a variable to store a reference to the Surface View at the main.xml file
    private SurfaceView sv;

    //a bitmap to display the captured image
    private Bitmap bmp;

    //Camera variables
    //a surface holder
    private SurfaceHolder sHolder;
    //a variable to control the camera
    private Camera mCamera;
    //the camera parameters
    private Parameters parameters;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        //get the Image View at the main.xml file
        iv_image = (ImageView) findViewById(R.id.imageView);

        //get the Surface View at the main.xml file
        sv = (SurfaceView) findViewById(R.id.surfaceView);

        //Get a surface
        sHolder = sv.getHolder();

        //add the callback interface methods defined below as the Surface View callbacks
        sHolder.addCallback(this);

        //tells Android that this surface will have its data constantly replaced
        sHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

    @Override
    public void surfaceChanged(SurfaceHolder arg0, int arg1, int arg2, int arg3)
    {
         //get camera parameters
         parameters = mCamera.getParameters();

         //set camera parameters
         mCamera.setParameters(parameters);
         mCamera.startPreview();

         //sets what code should be executed after the picture is taken
         Camera.PictureCallback mCall = new Camera.PictureCallback()
         {
             @Override
             public void onPictureTaken(byte[] data, Camera camera)
             {
                 //decode the data obtained by the camera into a Bitmap
                 bmp = BitmapFactory.decodeByteArray(data, 0, data.length);
                 //set the iv_image
                 iv_image.setImageBitmap(bmp);
             }
         };

         mCamera.takePicture(null, null, mCall);
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder)
    {
        // The Surface has been created, acquire the camera and tell it where
        // to draw the preview.
        mCamera = Camera.open();
        try {
           mCamera.setPreviewDisplay(holder);

        } catch (IOException exception) {
            mCamera.release();
            mCamera = null;
        }
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder)
    {
        //stop the preview
        mCamera.stopPreview();
        //release the camera
        mCamera.release();
        //unbind the camera from this object
        mCamera = null;
    }
}

reference: http://www.41post.com/3794/programming/android-take-a-picture-without-displaying-a-preview