how can i refresh the image ctrl???????

asp.net 2012.net.4 web.forms
adding dinamicly button and image control.
on button server click - i rotate the image 90 deg...
how can i refresh the image ctrl from server???????

i have shore the rotation do work, and i have tried to set the img url to empty and than the same url again...  
as well i using Response.Cache.SetCacheability(HttpCacheability.NoCache);

as will i have tried 
TextWriter tw = new StringWriter(); HtmlTextWriter hw = new HtmlTextWriter(tw); ((System.Web.UI.WebControls.Image)item).RenderControl(hw);