Style Attribute not taking effect until 1st postback

I've built a user control that displays an image (and then alters that image every few seconds).  One of the properties is 'Width'.  In the Page_Load event handler I have this code:

      if (!IsPostBack)
      {
        if (Width > 0)
          imagePhoto.Style.Add("width", Width.ToString());
      }
 
Here's the strange thing: It works BUT does NOT work with the first image, only the 2nd & subsequent images.
Why would that be?
Robert

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