Автор: http://www.swissdelphicenter.ch

{
  The example below demonstrates creating custom caret:
}

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  ExtCtrls, StdCtrls;

type
  TForm1 = class(TForm)
    Memo1: TMemo;
    Image1: TImage;
    Edit1: TEdit;
    procedure Memo1MouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure Edit1MouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.Memo1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  CreateCaret(Memo1.Handle, Image1.Picture.Bitmap.Handle, 0, 0);
  ShowCaret(Memo1.Handle);
end;

procedure TForm1.Edit1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  CreateCaret(Edit1.Handle, 0, 10, 4);
  ShowCaret(Edit1.Handle);
end;

end.

{The form file source (*.dfm) }

  object Form1: TForm1
    Left = 192
    Top = 107
    Width = 544
    Height = 375
    Caption = 'Form1'
    Color = clBtnFace
    Font.Charset = DEFAULT_CHARSET
    Font.Color = clWindowText
    Font.Height = -11
    Font.Name = 'MS Sans Serif'
    Font.Style = []
    OldCreateOrder = False
    PixelsPerInch = 96
    TextHeight = 13
    object Image1: TImage
      Left = 12
      Top = 4
      Width = 16
      Height = 16
      AutoSize = True
      Picture.Data = {  
      07544269746D6170B6020000424DB602000000000000B6000000280000001000  
      0000100000000100100000000000000200000000000000000000100000000000  
      000000000000000080000080000000808000800000008000800080800000C0C0  
      C000808080000000FF0000FF000000FFFF00FF000000FF00FF00FFFF0000FFFF  
      FF00000000000000000000000000000000000000000000000000000000000000  
      0000000000000000000000000000000000000000000000000000000000000000  
      000000000000FF7FFF7FFF7FFF7F000000000000FF7FFF7FFF7FFF7FFF7FFF7F  
      00000000FF7FFF7FFF7FFF7F000000000000FF7FFF7FFF7FFF7FFF7FFF7F0000  
      0000FF7FFF7FFF7FFF7FFF7F00000000FF7FFF7FFF7FFF7FFF7FFF7FFF7F0000  
      000000000000FF7FFF7FFF7F0000000000000000FF7FFF7FFF7FFF7F00000000  
      0000000000000000FF7FFF7FFF7FFF7FFF7FFF7FFF7FFF7FFF7FFF7F00000000  
      0000000000000000FF7FFF7FFF7FFF7FFF7FFF7FFF7FFF7FFF7F000000000000  
      0000000000000000FF7FFF7FFF7F00000000FF7FFF7FFF7FFF7F000000000000  
      00000000000000000000FF7FFF7FFF7FFF7FFF7FFF7FFF7F0000000000000000  
      00000000000000000000FF7FFF7FFF7FFF7FFF7FFF7FFF7F0000000000000000  
      000000000000000000000000FF7FFF7FFF7FFF7FFF7FFF7F0000000000000000  
      000000000000000000000000FF7FFF7FFF7FFF7FFF7F00000000000000000000  
      0000000000000000000000000000FF7FFF7FFF7FFF7F00000000000000000000  
      0000000000000000000000000000FF7FFF7FFF7F000000000000000000000000  
      00000000000000000000000000000000FF7F0000000000000000000000000000  
      0000}
    end
    object Memo1: TMemo
      Left = 12
      Top = 36
      Width = 149
      Height = 149
      Lines.Strings = ('Memo1')
      TabOrder = 0
      OnMouseDown = Memo1MouseDown
    end
    object Edit1: TEdit
      Left = 220
      Top = 60
      Width = 121
      Height = 21
      TabOrder = 1
      Text = 'Edit1'
      OnMouseDown = Edit1MouseDown
    end
  end