Detect multiple similar objects in a bunch of still images

edit

How could I separate the whole leaf into 5 independent leaf(blob)?The ultimate purpose is collect the BGR value of each leaf(leaf1, leaf2, leaf3, leaf4 and so on).

I am a newbie of computer vision, there are tons of algorithms I haven't learned yet. Any algorithms are possible to solve this problem?

Edit : According to the suggestion of GilLevi(thanks), i use houghLinesP to draw the lines on the image after segmentation.

//remove contours size which smaller than cmin or bigger than cmax
void remove_contours(std::vector<std::vector<cv::Point> > &contours, double cmin, double cmax)
{            
    auto it = std::partition(std::begin(contours), std::end(contours), [=](std::vector<cv::Point> const &data)
    {
       auto const size = cv::contourArea(data);
       return !(size < cmin || size > cmax);
    });
    contours.erase(it, std::end(contours));
}

void cut_to_single_leaf(cv::Mat const &input)
{    
    cv::Mat fore_ground_edge;
    cv::cvtColor(input, fore_ground_edge, CV_BGR2GRAY);
    cv::Canny(fore_ground_edge, fore_ground_edge, 100, 350);        

    cv::Mat result = input.clone();
    std::vector<cv::Vec4i> lines;
    cv::HoughLinesP(fore_ground_edge, lines, 1, CV_PI/180, 80, 0, 40);
    for( auto const &line : lines){
        cv::line(result, cv::Point(line[0], line[1]),
                cv::Point(line[2], line[3]), cv::Scalar(0,0,0), 2, 8);
    }

    cv::Mat binary_result;
    cv::cvtColor(result, binary_result, CV_BGR2GRAY);
    ContoursType contours;
    cv::findContours(binary_result, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);
    gray_result.setTo(0);
    OCV::remove_contours(contours, 500, 50000);
    std::cout<<contours.size()<<std::endl;
    cv::drawContours(binary_result, contours, -1, cv::Scalar(255), 2);         

    cv::waitKey();
}

The results(use first image as an example)

The results are far from perfect. The leftmost leaf are separated to two leafs. The center leaf are glue as one leaf.

Question 1 : Any good idea to find out which contours should merge together? ex : leftmost contours should apply dilation since it is splited to two leafts

Question 2 : How could I open the leaf of center? try erosion and open, but the results are not good, hard to predict

Question 3 : Any other algorithms are good to detect multiple similar objects in a still image? just study SIFT and SURF, they could not detect multiple objects in a still image. I can not separate the image into different ROI and apply SIFT or SURF, because the orientation of the leafs are different in the images.