PImage subject;
float baseStart;
float baseLength;
float xVector;
float yVector;
float hStart;
float hLength;

void setup() {
  size(600, 440);
  background(128);
  subject = loadImage("trey.jpg");
  image(subject, 0, 0);
  stroke(0, 0, 0, 75);
  smooth();
  baseStart = 3;
  baseLength = 20;
}

void draw() {
  hStart = random(-baseStart, baseStart);
  hLength = random(baseLength);

  if (mousePressed == true) {

    if (mouseX>=width/2) {
      xVector = random(hLength);
    } else {
      xVector = -random(hLength);
    }

    if (mouseY>=height/2) {
      yVector = random(hLength);
    } else {
      yVector = -random(hLength);
    }

    line(mouseX+hStart, mouseY+hStart, mouseX+xVector, mouseY+yVector);
  }
}