you'll have to cycle inside every image with a for cycle looking for the brightest (or greenest, or whatsoever) pixel; something like this should work:
Code:

for(x=imgX; x<imgWidth; x++){
   for(y=imgY; y<imgHeight; y++){
	if(brightness(pixels[width*y+x])>maxImgBright){
	    maxImgBright = brightness(pixels[width*y+x];
	    brightX = x;
	    brightY = y;
	}
   }
}
 

you should probably create a class to store the images and the "brightest point" routine, then you'll simply have to draw lines between every image.brightX and image.brightY point.

ciao!