C# – Best way to make sure the user dont upload images more than 1MB in size

In C# 5 and earlier, to give auto implemented properties an initial value, you have to do it in a constructor.

Since C# 6.0, you can specify initial value in-line. The syntax is:

public int X { get; set; } = x; // C# 6 or higher

DefaultValueAttribute is intended to be used by the VS designer (or any other consumer) to specify a default value, not an initial value. (Even if in designed object, initial value is the default value).

At compile time DefaultValueAttribute will not impact the generated IL and it will not be read to initialize the property to that value (see DefaultValue attribute is not working with my Auto Property).

Example of attributes that impact the IL are ThreadStaticAttribute, CallerMemberNameAttribute, ...

I believe the Path attribute shouldn't start or end with a "/" - so you should have:

<location path="File">
  <system.web>
    <httpRuntime executionTimeout="60" maxRequestLength="4096" />
  </system.web>
</location>
<location path="Picture">
  <system.web>
    <httpRuntime executionTimeout="60" maxRequestLength="1024" />
  </system.web>
</location>

Your virtual or physical directory–level Web.config's shouldn't have the <location> elements.

That should sort you out.

The docs for the Location element even have this very example:

The following code example demonstrates how to set the uploaded file size limit to 128 KB for only the page specified.

<configuration>
  <location path="UploadPage.aspx">
    <system.web>
      <httpRuntime maxRequestLength="128"/>
    </system.web>
  </location>
</configuration>