and this is the code itself that i'm trying to figure that out
Code:

import hypermedia.video.*;

OpenCV opencv;

Capture cameraFrame;
PImage previousFrame;
PImage currentFrame;
PImage differenceFrame;
PImage displayFrame;

MovieMaker mm;
color[][] clre;
PVector[][] posizioni;

PVector origin;
ArrayList particles = new ArrayList();
int numParticles = 10000;
int z = 0; 

void setup()
{
  size(640, 480);
  colorMode(HSB, 360, 100, 100, 100);
  PFont font = createFont("sansSerif", 12); 
  textFont(font, 24); 
  clre = new color[width][height/2];
  posizioni = new PVector[width][height/2];
  //mm = new MovieMaker(this, width, height, "drawing.mov", 30, MovieMaker.VIDEO, MovieMaker.LOSSLESS);

  cameraFrame = new Capture(this, width, height,30);
  previousFrame = new PImage(width, height);
  currentFrame = new PImage(width, height);
  differenceFrame = new PImage(width, height);
  displayFrame = new PImage(width, height);
  
}

void draw()
{
  opencv.read();                               // grab frame from camera
    opencv.absDiff();                            // make the difference between the current image and the image in memory
    opencv.remember();                            //remember the current image into memory
    opencv.convert(OpenCV.GRAY);                  //convert the image to grayscale
    opencv.threshold(80);                          //apply a threshold filers
    image( opencv.image(), 0, 0 );             // display the result 
  
  
   //get all the blobs and store them in the array. Value are blobs(minArea, maxArea, maxNumBlobs, findHoles);
    Blob[] blobs = opencv.blobs( 50, width*height/3, 20, false );
    //count throught the array
     for( int i=0; i<blobs.length; i++ ) {
        //get the rectange shape and the centroids (centres)
        Rectangle bounding_rect	= blobs[i].rectangle;
        Point centroid = blobs[i].centroid;

        // display rectangles
        noFill();
       // A shortcut for writing an if and else structure. 
       //If the condition evaluates to true, the first value is 
       //evaluated and returned. If the condition evaluates to 
       //false, the second is evaluated and returned. 
        
        stroke( blobs[i].isHole ? 128 : 64 );
        rect( bounding_rect.x, bounding_rect.y, bounding_rect.width, bounding_rect.height );

        // display centroids (centres)
        stroke(0,0,255);
        line( centroid.x-5, centroid.y, centroid.x+5, centroid.y );
        line( centroid.x, centroid.y-5, centroid.x, centroid.y+5 );
        
    }
  //this code below is the original code
 // background(1, 0, 100,255); // set the background to white
  
  textAlign(CENTER);
  fill(1, 100, 100, 1); // color of the particle, particle fill maybe

  text("Human,"+'\n'+"We are just no more than dust." , width/2, 50);
  

 for(int i=0; i<width; i++) {
    for(int j = 0; j<height/2; j++) {
       clre[i][j] = get(i,j);
       if(clre[i][j] != -1){
            if(z < numParticles){
            posizioni[i][j] = new PVector(i,j,0);  
            origin = new PVector(posizioni[i][j].x, 130+posizioni[i][j].y, 0);
            PVector a = new PVector();
            PVector v = new PVector();        
            PVector l = new PVector(random(width), random(height) , 0);
            particles.add(new Particle(a,v,l, origin, random(0.05f, 2.0f)));
            z++;
            }
      }
    }
  }
          for (int h = 0; h<particles.size()-1; h++){
            Particle prt = (Particle) particles.get(h);
            prt.run();
            
            PVector actualVel = prt.getVelocity(); 
            PVector attrito = PVector.mult(actualVel,-0.05); 
            prt.add_force(attrito);
            
            
            //need to change code below to display the text without pressing a, as default
      //      if(keyPressed) { 
        //       if (key == 'a' || key == 'A')
          //    { 
                PVector origLoc = prt.getOrigin();
                PVector diff = PVector.sub(origLoc,prt.getLocation()); 
                diff.normalize(); 
                float factor = 0.5f;  
                diff.mult(factor); 
                prt.setAcceleration(diff); 
              }
              
               /*
               if (key == ' ' || key == ' ')
              { 
               mm.finish();
              }  
                */            
            } 
            
            //need to change code below to map into camera , movement detection
           // if(mousePressed) {  
              //instead of mousePressed
              //check to see if on black or white
              //prt.getLocation (work out how to get the x and y point
              //get the colour of the pixel at that location
              //if on white don't move
              //if on black move
              //x is 20 and y is 20
              //int prtx = the location of the particle int()
              //int prty = the location of the particle
              PVector prtPos = prt.getLocation();
              color prtColor = displayFrame.get(opencv.absDiff);
              
              //red(), green(), blue
              //if (prtRed >=253 && prtGreen >=253 && prtBlue > 253
              //pixel must be white! so don't move
              //else
              //pixel is black
              //
              
              
              PVector mouseLoc = new PVector(mouseX, mouseY, 0);
              PVector diff = opencv.absDiff;
              diff.normalize(); 
              float factor = 1.0f;  
              diff.mult(factor); 
              prt.setAcceleration(diff); 
              
            } 
          }

}



 

That's a lot of code not everybody can even run (need to have the library and probably some video device...).
And at a glance, I can't say want is your problem ("doesnt wrok" isn't very explicit...).

BTW, I wonder why you ask that in the Syntax Questions section instead of the Video one... (where perhaps more knowledgeable people might look).