C# windows application with restrict print screen and screen recording

To disable screen capture in a Windows Forms desktop application using C#, you can employ techniques such as using window attributes or direct APIs that restrict screen capture.

Below are approaches you can use:

1. Use the SetWindowDisplayAffinity API (Windows 8 and later)

The SetWindowDisplayAffinity function prevents screen capture by marking the window as non-screen-capturable. This works for tools like Snipping Tool or Print Screen, but it may not stop all third-party screen recording tools.

Implementation

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;

public class MainForm : Form
{
    // Import the SetWindowDisplayAffinity function
    [DllImport("user32.dll")]
    private static extern bool SetWindowDisplayAffinity(IntPtr hWnd, uint affinity);

    // Constants for display affinity
    private const uint WDA_NONE = 0;
    private const uint WDA_MONITOR = 1;

    protected override void OnHandleCreated(EventArgs e)
    {
        base.OnHandleCreated(e);

        // Set the window to prevent screen capture
        SetWindowDisplayAffinity(this.Handle, WDA_MONITOR);
    }

    protected override void OnFormClosed(FormClosedEventArgs e)
    {
        // Reset the display affinity when the form is closed
        SetWindowDisplayAffinity(this.Handle, WDA_NONE);
        base.OnFormClosed(e);
    }

    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new MainForm());
    }
}

2. Black Out Sensitive Content on Minimized

Instead of preventing screen capture, you can obscure sensitive content when the application is minimized or not in focus.

Implementation

protected override void OnResize(EventArgs e)
{
    base.OnResize(e);
    if (this.WindowState == FormWindowState.Minimized)
    {
        // Hide sensitive content or overlay with black
        this.Opacity = 0; // Makes the window invisible
    }
    else
    {
        this.Opacity = 1; // Restore visibility
    }
}

3. Block Screen Capture via Registry (Group Policy)

While not a code-level solution, you can modify Windows Group Policies or registry keys to restrict screen capture for specific applications. This requires admin privileges and might not be app-specific.

Limitations

• SetWindowDisplayAffinity only works on systems with DWM (Desktop Window Manager) enabled and might not block all screen capture tools.
• Third-party screen recording software or hardware-based capture devices may bypass these restrictions.
• Overuse of such techniques can lead to a poor user experience.

Best Practices

• Use these techniques sparingly, only for applications handling sensitive or confidential data.
• Consider complementing this with user agreements and legal notices to discourage unauthorized screen capture or recording.