How to retrieve the visible texture from a png image in cocos2d-x

I am making a question answer game in which the answer images are made as sprites from png images.

The answer image is like this:

I am making rect on the image like this:

Rect rect = Rect(answerSprites.at(i)->getBoundingBox().origin.x,
                    answerSprites.at(i)->getBoundingBox().origin.y,
                    answerSprites.at(i)->getBoundingBox().size.width,
                    answerSprites.at(i)->getBoundingBox().size.height);

Then i am detecting touch on the rect as :

void HelloWorld::onTouchesBegan(const std::vector<Touch*>& touches,
        Event *unused_event) {
    auto target = static_cast<Sprite*>(unused_event->getCurrentTarget());
    auto touchPointBegan = (Touch*) touches.front();
    Vec2 locationBegan = touchPointEnded->getLocation();
    Point locationInNode = target->convertToNodeSpace(locationEnded);
    Size s = target->getContentSize();
        if (rect.containsPoint(locationInNode)) {
            log(“Correct Touch”);
        }
}

The code is working fine but the problem is that it is detecting the touch on the full png, but i want to detect the touch on the flower only. The flower can be at any position on the png.

How can i make the rect only on the flower?

Check the transparency of the touch location with this code:

// Answer sprite
m_sprite = Sprite::create("answer-1.png");
m_sprite->setPosition( Vec2(winSize.width*.5, winSize.height*.5)  );
addChild(m_sprite);

bool HelloWorld::onTouchBegan(const cocos2d::Touch *touch, cocos2d::Event *event)
{
    _originPoint = touch->getLocation();
    _destinationPoint = _originPoint;

    Vec2 locationInNode = m_sprite->convertToNodeSpace(touch->getLocation());

    Rect rect = Rect(m_sprite->getBoundingBox().origin.x,
                     m_sprite->getBoundingBox().origin.y,
                     m_sprite->getContentSize().width,
                     m_sprite->getContentSize().height);


    if (rect.containsPoint(touch->getLocation() )) {

        if (tapsOnNonTransparent(locationInNode, "answer-1.png" )) {
            log("Correct Touch");
        }

    }

    return true;
}

const bool HelloWorld::tapsOnNonTransparent( const cocos2d::Point& tap, const std::string &spritePath )
{
    auto imgPtr = std::make_unique<cocos2d::Image>();
    imgPtr->initWithImageFile( spritePath );

    const int width = imgPtr ->getWidth();
    const int height = imgPtr ->getHeight();

    unsigned x = unsigned( tap.x ) % width;
    /// Don't forget to invert y coordinate.
    unsigned y = unsigned( height - tap.y ) % height;
    unsigned index = x + y * width;
    unsigned dataLen = imgPtr ->getDataLen();
    CCAssert( index < dataLen, "index is bigger than image size." );
    unsigned char* pixel = imgPtr->getData() + (4 * index);
    return !isZeroPixel( pixel );
}

const bool HelloWorld::isZeroPixel( const unsigned char* pixel )
{
    return 0 == pixel[0] && 0 == pixel[1] && 0 == pixel[2] && 0 == pixel[3];
}