How to hide the main panel and show an image over the whole page?

You need to hide the Bevel1, MainPanel and the InnerNotebook components when you switch to your welcome page and show them again when you leave it. As the opposite, the image you need to show only when you’re showing your welcome page since it covers the whole page area. So the following code will do the trick:

[Code]
var
  WelcomePageID: Integer;
  BitmapImage: TBitmapImage;

procedure InitializeWizard;
var
  WelcomePage: TWizardPage;  
begin
  WelcomePage := CreateCustomPage(wpWelcome, '', '');
  WelcomePageID := WelcomePage.ID;
  BitmapImage := TBitmapImage.Create(WizardForm);
  BitmapImage.Bitmap.LoadFromFile('C:\Image.bmp');
  BitmapImage.Top := 0;
  BitmapImage.Left := 0;
  BitmapImage.AutoSize := True;
  BitmapImage.Cursor := crHand;
  BitmapImage.Visible := False;
  BitmapImage.Parent := WizardForm.InnerPage;
end;

procedure CurPageChanged(CurPageID: Integer);
begin
  BitmapImage.Visible := CurPageID = WelcomePageID;
  WizardForm.Bevel1.Visible := CurPageID <> WelcomePageID;
  WizardForm.MainPanel.Visible := CurPageID <> WelcomePageID;
  WizardForm.InnerNotebook.Visible := CurPageID <> WelcomePageID;
end;