How would you send clock impulses to a camera with an Arduino Mega?
It depends on the camera that you're using but you send in impulse just sending digital write signal, waiting a little bit and then turning it off. You do this over and over again until you have all the pixels. Here is an example where I send 128 impulses:

  for(int i = 0; i &lt; 128; i++)
  {
    digitalWrite(CLK, HIGH);
    delay(1);  
    digitalWrite(CLK, LOW);
    delay(1);
  }


Depending on the hardware you are using you might have to send a SI (signal impulse) prior to the CLK impulses and the delay in between them will vary. The best thing to do is to read the documentation to find these figures.