You can specify certain folders or paths in your application to be accessible by all users, specially when you are using windows forms authentication for instance, below is an example which grants access to all users on a certain page called register.aspx and the images folder:
<system.web>
...
...
<location path="register.aspx">
<system.web>
<authorization>
<allow users="*" /> // this will allow access to everyone to register.aspx
</authorization>
</system.web>
</location>
<location path="Images">
<system.web>
<authorization>
<allow users="*" /> // this will allow access to everyone to Images folder
</authorization>
</system.web>
</location>
</system.web>