title: Refresh image or clear cache
body: <p>Is there any way (server or client side) to force the browser to pull a new version of a file (image) from the server. The image in question is otherwise cached for a long time. I know I can append a random number, for instance, to the URL of the image but this is not acceptable in this situation. I need for the image to be refresh from the <strong>exact same</strong> URL.</p>
  
  <p>What I'm doing: a YouTube like portal where users upload videos. Each video has a thumbnail which is shown on various pages on the portal. User can, at any time, change the thumbnail (he can select from three generated thumbnails). So when this happens (a new image overwrites the 'original' image), I wan't to refresh the video's thumbnail so that the owner (I don't care if other users see the old thumbnail) will see the new thumbnail no matter where the thumbnail is shown.</p>
  
  <p>I'm afraid this can't be done but I'm asking here just to be sure.</p>
  
  <p>update: I'm using nginx and PHP on the server side</p>