random selection from an array

First place this static field in your form class:

   static Random rand = new Random();

Suppose now that 'images' is your Image array and that 'pictureBoxes' is your PictureBox array. I'm assuimg that the number of pictureboxes is less than or equal to the number of images. The following code will place a (different) random image in each PictureBox:

   bool[] isUsed = new bool[images.Length]; // all false by default
   int index = 0;
   do
   {
      int imageNum = rand.Next(0, images.Length); // includes 0 but excludes images.Length
      if (!isUsed[imageNum])
      {
         pictureBoxes[index].Image = images[imageNum];
         isUsed[imageNum] = true;
         index++;
      }
   }
   while (index < pictureBoxes.Length);