You can not do like this in .aspx page
The alternative is you can write the following code in ur .aspx.cs page.
In Page Load Event write the code to get the value from hiddenfield and assign it to the imageurl property if the image or in the javascript also
sample code to do in pageload event
protected void Page_Load(object sender, EventArgs e)
{
Image.ImageUrl = hdID.Value;
}