I ran across a need to make sure an image on a webpage loaded from the server on each load of the page.  This was accomplished by loading the images with a random number as a parameter.
So it ended up looking like:  <img src=”>

In PHP this was done by adding:  ?<?php echo rand(1000,7000)?> to the image source.

In (VB):  Using an asp:image with id =”Image1″ on the page.
VB code behind:
If Not Me.IsPostBack Then
Dim randImgNum As Integer
randImgNum = RandomNumber(1000,7000)
Me.Image1.ImageUrl = “” & randImgNun
end if