function randomNumber(limit){
  return Math.floor(Math.random()*limit);
}

function randomImage(imgArr)
{
  var imgSrc;
  var r;
  r = randomNumber(imgArr.length);
  imgSrc = imgArr[r];
  
  document.write('<img src="' + imgSrc + '" alt="products" class="picR" />');
  
}

randomImage( [ 
	"images/foodstorage.jpg" , 
	"images/medical.jpg" , 
	"images/industrial.jpg" , 
	"images/architech.jpg" , 
	"images/goverment.jpg" , 
	"images/iProtectionSuit.jpg" , 
	] );