Please note that if you use relative paths for images on your master page then those relative paths are relative to the path of the actual aspx pages that use this master page. Most probably your paths are relative to the presence of master page. The best way to deal with this scenario is to use server image control with following kind of syntax:
<asp:Image id="i1" runat="server" ImageUrl="~/Images/Image1.gif" EnableViewState="false" />
using a "~/" automatically begins with the root of the virtual path. However if you are using html img control without using runat=server then you won't be able to use the~/ syntax, in such cases you may come up with a custom function in lines with these link
http://forums.asp.net/t/1374426.aspx/1[
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ResolveUrl in ASP.NET - The Perfect Solution[
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Regards
Pawan