Erasing multiple pictureboxes

Question

So, I have a random number generator that slects a random location for a picturebox. I also want to have a timer so that everyone 1 minute those images get replaced with other images in random locations. So far I have the random number generator and the images get placed randomly. Great! , but whenever the minute passes those images stay there and instead of getting replaced new pictureboxes appear on top of them. 

 

   

   void RefreshTimer_Tick(object sender, EventArgs e)

   {

   r = 15;

   Button1_Click(this, null);

   MessageBox.Show("Refreshed");

   }

 

   if (r == 15)

    {

   do

   {

   theImage.Image = null;

   r--;

   }

   while (r == 15);

   }

 (PS its 15 because there are 15 images)

 

Why doesn't this work?