Rectangle

function Rectangle(const rec: TRect): TPathD; overload;

function Rectangle(const rec: TRectD): TPathD; overload;

function Rectangle(l, t, r, b: double): TPathD; overload;

This function returns the points representing the rectangle's 4 corners: top-left, top-right, bottom-right & bottom-left (in that order).

uses Img32, Img32.Fmt.PNG, 
  Img32.Vector, Img32.Transform;
...
var
  img: TImage32;
  dst: TPathD;
begin
  img := TImage32.Create;
  img.LoadFromFile('clouds.png');
  
  //setup the transformation geometry
  dst := Rectangle(src.Bounds); 
  dst[0].Y := 20;
  dst[3].Y := img.Height-20; 
  
  //transform and save
  ProjectiveTransform(img, dst);
  img.SaveToFile('clouds_proj.png');
  img.Free;
end;