I am doing an application of the concept of the dodgeball and need to test of the pixel of the ball is in the blobs capture(which is the image of the player) I am stucked and ran out of idea of how to implement it. I manage to do a little progress which have the blobs but I not sure how to test it. Please help. I am a newbie who in a desperate condition. Thank you.

This is some of my code.

void testApp::setup(){

#ifdef _USE_LIVE_VIDEO
    vidGrabber.setVerbose(true);
    vidGrabber.initGrabber(widthS,heightS);
#else
    vidPlayer.loadMovie("fingers.mov");
    vidPlayer.play();
#endif
widthS = 320;
heightS = 240;
colorImg.allocate(widthS,heightS);
grayImage.allocate(widthS,heightS);
grayBg.allocate(widthS,heightS);
grayDiff.allocate(widthS,heightS); ////<---what I want

bLearnBakground = true;
threshold = 80;

//////////circle//////////////
counter = 0;
radius = 0;
circlePosX = 100;
circlePosY=200;

}

void testApp::update(){

ofBackground(100,100,100);

bool bNewFrame = false;

#ifdef _USE_LIVE_VIDEO
   vidGrabber.grabFrame();
   bNewFrame = vidGrabber.isFrameNew();
#else
    vidPlayer.idleMovie();
    bNewFrame = vidPlayer.isFrameNew();
#endif

if (bNewFrame){

    if (bLearnBakground == true){
        grayBg = grayImage;     // the = sign copys the pixels from grayImage into grayBg (operator overloading)
        bLearnBakground = false;
    }

    #ifdef _USE_LIVE_VIDEO
        colorImg.setFromPixels(vidGrabber.getPixels(),widthS,heightS);
    #else
        colorImg.setFromPixels(vidPlayer.getPixels(),widthS,heightS);
    #endif

    grayImage = colorImg;

    grayDiff.absDiff(grayBg, grayImage);
    grayDiff.threshold(threshold);

    contourFinder.findContours(grayDiff, 20, (340*240)/3, 10, true);    // find holes
}



////////////circle////////////////////
counter = counter + 0.05f;
if(radius>=50){
    circlePosX = ofRandom(10,300);
    circlePosY = ofRandom(10,230);
}
radius = 5 + 3*(counter);

}

void testApp::draw(){

// draw the incoming, the grayscale, the bg and the thresholded difference
ofSetColor(0xffffff); //white colour
grayDiff.draw(10,10);// draw start from point (0,0);
// we could draw the whole contour finder

// or, instead we can draw each blob individually,
// this is how to get access to them:
for (int i = 0; i < contourFinder.nBlobs; i++){
    contourFinder.blobs[i].draw(10,10);

}

///////////////circle//////////////////////////
//let's draw a circle:
ofSetColor(0,0,255);
char buffer[255];
float a = radius;
sprintf(buffer,"radius = %i",a);
ofDrawBitmapString(buffer, 120, 300);

if(radius>=50)
 {
    ofSetColor(255,255,255);
    counter = 0;
 }
 else{

    ofSetColor(255,0,0);

 }
 ofFill();
 ofCircle(circlePosX,circlePosY,radius);

}