How to display custom Image in WinForms MessageBoxAdv control?
Display the custom image
The MessageBoxAdv control provides support to display custom images in it and that can be achieved by using its function named Show.
C#
// Support Icon
MessageBoxAdv.Show("Metro Theme Customization", "This is Syncfusion MessageBoxAdv Control", MessageBoxButtons.OKCancel,this.imageListAdv1.Images[0],new Size(50, 50));
VB
' Support Icon
MessageBoxAdv.Show("Metro Theme Customization", "This is Syncfusion MessageBoxAdv Control", MessageBoxButtons.OKCancel, Me.imageListAdv1.Images(0), New Size(50, 50))
Screenshot

Figure 1: Custom Icon.
Samples:
Reference link: https://help.syncfusion.com/windowsforms/messagebox/button-parameters#icon