Thanks for your response. I solved the problem of images by using Url Type as "Root Relative" instead of "Document Relative" 

I have one more doubts 

 We rewrite the url in Application_BeginRequest()

Suppose we want to rewrite the url  "questions.aspx?tid=1" as  "MathsQestions.aspx"

We do this by calling  'MathsQestions.aspx' when we need to call 'questions.aspx?tid=1' and rewte the url    "MathsQestions.aspx" to questions.aspx?tid=1' on Application_BeginRequest()

My question is that  how can i identify the value of 'tid' at Application_BeginRequest()?

since we cant pass values in session or context.items. Because we cannt access session and context.items at Application_BeginRequest().

Then how can we do it? Do you have any solution?(Note that i am usint .net 1.1)

I think it is not possibe. And i desided to embedd the value of' 'tid'  in the new url as:use  '1_MathsQestions.aspx' instead of 'MathsQestions.aspx'

which means tid=1.