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procedure SetBackground(aForm: TForm; aPath: String; aStretch: Boolean);
var
BkgrndImage: TImage;
begin
BkgrndImage := TImage.Create(aForm);
BkgrndImage.Align := alClient;
BkgrndImage.Parent := aForm;
BkgrndImage.Picture.LoadFromFile(aPath);
BkgrndImage.Stretch := aStretch;
end;                    

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procedure ClearBackground(aForm: TForm);
begin
with TImage(aForm.FindComponent('BkgrndImage')) do Free;
end;                    

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procedure TForm1.Button1Click(Sender: TObject);
begin
SetBackground(Form1, 'C:\asd.bmp', True);
end;                    

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procedure TForm1.Button2Click(Sender: TObject);
begin
ClearBackground(Form1);
end;