사각형은 그냥Rectangle() 사용 하여서 그리면 되지 않을까 싶네요
원같은 경우에는 Ellipse() 사용 하시면 될거 같구요

김준석 님이 쓰신 글 :
:

: //---------------------------------------------------------------------------
: 
: #include 
: #pragma hdrstop
: 
: #include "Unit1.h"
: //---------------------------------------------------------------------------
: #pragma package(smart_init)
: #pragma link "CGRID"
: #pragma resource "*.dfm"
: int a = 0;
: TForm1 *Form1;
: TPoint MPoint, StartDot;
: //---------------------------------------------------------------------------
: __fastcall TForm1::TForm1(TComponent* Owner)
:         : TForm(Owner)
: {
: }
: //---------------------------------------------------------------------------
: 
: void __fastcall TForm1::FormCreate(TObject *Sender)
: {
:         Image1->Picture->Bitmap->Height =  305;
:         Image1->Picture->Bitmap->Width = 320;
:         ListBox1->ItemIndex = 0;
: 
:         this->DoubleBuffered=true;
: 
: }
: //---------------------------------------------------------------------------
: TPoint stPt1,stPt2;   
: int iPBrushWid=3;
: void __fastcall TForm1::Image1MouseMove(TObject *Sender, TShiftState Shift,
:       int X, int Y)
: {
:         if(Shift.Contains(ssLeft)){
:         if(a==1){  // 연필
:         Image1->Picture->Bitmap->Canvas->LineTo(X,Y);
:         }
:         if(a==2){ // 빗금
:         TPoint cuPt1,cuPt2,cuPt3,cuPt4;
:         cuPt1=Point(X-iPBrushWid,Y-iPBrushWid);
:         cuPt2=Point(X+iPBrushWid,Y+iPBrushWid);
: 
:         TPoint p[5]={stPt1,stPt2,cuPt2,cuPt1,stPt1};
:         Image1->Canvas->Polygon(&p[0],4);
:         stPt1=cuPt1;
:         stPt2=cuPt2;
:         }
:         if(a==3)//사각형
:         {
: 
:         }
:         }
: }
: //---------------------------------------------------------------------------
: 
: void __fastcall TForm1::Image1MouseDown(TObject *Sender,
:       TMouseButton Button, TShiftState Shift, int X, int Y)
: {
:         Image1->Canvas->Brush->Color= CColorGrid1->ForegroundColor;
:         Image1->Picture->Bitmap->Canvas->Pen->Color = CColorGrid1->ForegroundColor;
:         Image1->Picture->Bitmap->Canvas->Pen->Width = ListBox1->ItemIndex+1;
:         if(a==1){
:         Image1->Picture->Bitmap->Canvas->MoveTo(X,Y);}
:         if(a==2){
:         stPt1=Point(X-iPBrushWid,Y-iPBrushWid);
:         stPt2=Point(X+iPBrushWid,Y+iPBrushWid);
:         }
:         if(a==3){
: 
: 
:         }
: 
: 
: }
: //---------------------------------------------------------------------------
: void __fastcall TForm1::Button1Click(TObject *Sender)
: {
:         if (SaveDialog1->Execute())
: 	Image1->Picture->Bitmap->SaveToFile(SaveDialog1->FileName);
: }
: //---------------------------------------------------------------------------
: void __fastcall TForm1::Button2Click(TObject *Sender)
: {
:         if (OpenDialog1->Execute())
: 	Image1->Picture->Bitmap->LoadFromFile(OpenDialog1->FileName);
: }
: //---------------------------------------------------------------------------
: 
: 
: void __fastcall TForm1::SpeedButton1Click(TObject *Sender)
: {
:         a = 2;
: }
: //---------------------------------------------------------------------------
: 
: void __fastcall TForm1::SpeedButton3Click(TObject *Sender)
: {
:         a = 1;
: }
: //---------------------------------------------------------------------------
: 
: void __fastcall TForm1::SpeedButton2Click(TObject *Sender)
: {
:         a = 3;
: }
: //---------------------------------------------------------------------------
: