How to pick an image from gallery (SD Card) for my app?

private static final int SELECT_PHOTO = 100;

Start intent

Intent photoPickerIntent = new Intent(Intent.ACTION_PICK);
photoPickerIntent.setType("image/*");
startActivityForResult(photoPickerIntent, SELECT_PHOTO);    

Process result

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent imageReturnedIntent) { 
    super.onActivityResult(requestCode, resultCode, imageReturnedIntent); 

    switch(requestCode) { 
    case SELECT_PHOTO:
        if(resultCode == RESULT_OK){  
            Uri selectedImage = imageReturnedIntent.getData();
            InputStream imageStream = getContentResolver().openInputStream(selectedImage);
            Bitmap yourSelectedImage = BitmapFactory.decodeStream(imageStream);
        }
    }
}

Alternatively, you can also downsample your image to avoid OutOfMemory errors.

private Bitmap decodeUri(Uri selectedImage) throws FileNotFoundException {

        // Decode image size
        BitmapFactory.Options o = new BitmapFactory.Options();
        o.inJustDecodeBounds = true;
        BitmapFactory.decodeStream(getContentResolver().openInputStream(selectedImage), null, o);

        // The new size we want to scale to
        final int REQUIRED_SIZE = 140;

        // Find the correct scale value. It should be the power of 2.
        int width_tmp = o.outWidth, height_tmp = o.outHeight;
        int scale = 1;
        while (true) {
            if (width_tmp / 2 < REQUIRED_SIZE
               || height_tmp / 2 < REQUIRED_SIZE) {
                break;
            }
            width_tmp /= 2;
            height_tmp /= 2;
            scale *= 2;
        }

        // Decode with inSampleSize
        BitmapFactory.Options o2 = new BitmapFactory.Options();
        o2.inSampleSize = scale;
        return BitmapFactory.decodeStream(getContentResolver().openInputStream(selectedImage), null, o2);

    }

Updated answer, nearly 5 years later:

The code in the original answer no longer works reliably, as images from various sources sometimes return with a different content URI, i.e. content:// rather than file://. A better solution is to simply use context.getContentResolver().openInputStream(intent.getData()), as that will return an InputStream that you can handle as you choose.

For example, BitmapFactory.decodeStream() works perfectly in this situation, as you can also then use the Options and inSampleSize field to downsample large images and avoid memory problems.

However, things like Google Drive return URIs to images which have not actually been downloaded yet. Therefore you need to perform the getContentResolver() code on a background thread.

---

Original answer:

The other answers explained how to send the intent, but they didn't explain well how to handle the response. Here's some sample code on how to do that:

protected void onActivityResult(int requestCode, int resultCode, 
       Intent imageReturnedIntent) {
    super.onActivityResult(requestCode, resultCode, imageReturnedIntent); 

    switch(requestCode) { 
    case REQ_CODE_PICK_IMAGE:
        if(resultCode == RESULT_OK){  
            Uri selectedImage = imageReturnedIntent.getData();
            String[] filePathColumn = {MediaStore.Images.Media.DATA};

            Cursor cursor = getContentResolver().query(
                               selectedImage, filePathColumn, null, null, null);
            cursor.moveToFirst();

            int columnIndex = cursor.getColumnIndex(filePathColumn[0]);
            String filePath = cursor.getString(columnIndex);
            cursor.close();


            Bitmap yourSelectedImage = BitmapFactory.decodeFile(filePath);
        }
    }
}

After this, you've got the selected image stored in "yourSelectedImage" to do whatever you want with. This code works by getting the location of the image in the ContentResolver database, but that on its own isn't enough. Each image has about 18 columns of information, ranging from its filepath to 'date last modified' to the GPS coordinates of where the photo was taken, though many of the fields aren't actually used.

To save time as you don't actually need the other fields, cursor search is done with a filter. The filter works by specifying the name of the column you want, MediaStore.Images.Media.DATA, which is the path, and then giving that string[] to the cursor query. The cursor query returns with the path, but you don't know which column it's in until you use the columnIndex code. That simply gets the number of the column based on its name, the same one used in the filtering process. Once you've got that, you're finally able to decode the image into a bitmap with the last line of code I gave.

You have to start the gallery intent for a result.

Intent i = new Intent(Intent.ACTION_PICK,
               android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
startActivityForResult(i, ACTIVITY_SELECT_IMAGE); 

Then in onActivityForResult, call intent.getData() to get the Uri of the Image. Then you need to get the Image from the ContentProvider.