モバイルの場合には TCameraComponent.Kind プロパティで前面/背面カメラを切り替えられるのですが、Windows の場合には USB 外付けカメラが使える事もあって Kind プロパティでの変更はできない事が多いです。以下のユニットを使えばカメラを任意で切り替える事ができます。

[FMX.CameraComponentEx]

unit FMX.CameraComponentEx;

interface

uses
  System.Classes, FMX.Media;

type
  { TCameraComponentHelper }
  TCameraComponentHelper = class helper for TCameraComponent
  private
    procedure SetCameraDevice(const Value: TCaptureDevice);
    function GetCameraDevice: TCaptureDevice;
  public
    property CameraDevice: TCaptureDevice read GetCameraDevice write SetCameraDevice;
  end;

  { TCameraList }
  TCameraList = class
  private
    FCamList: TStringList;
    FCount: Integer;
    function GetItems(Index: Integer): TCaptureDevice;
  public
    constructor Create;
    destructor Destroy; override;
    property Count: Integer read FCount;
    property Items[Index: Integer]: TCaptureDevice read GetItems;
  end;

implementation

{ TCameraComponentHelper }

function TCameraComponentHelper.GetCameraDevice: TCaptureDevice;
begin
  result := Self.FDevice;
end;

procedure TCameraComponentHelper.SetCameraDevice(const Value: TCaptureDevice);
begin
  Self.FDevice := TVideoCaptureDevice(Value);
end;

{ TCameraList }

constructor TCameraList.Create;
var
  CaptureDeviceList: TCaptureDeviceList;
  i: Integer;
begin
  {$IFDEF MACOS}
  DefaultSystemCodePage := 65001;
  {$ENDIF}
  FCamList := TStringList.Create;
  CaptureDeviceList := TCaptureDeviceManager.Current.GetDevicesByMediaType(TMediaType.Video);
  for i:=0 to CaptureDeviceList.Count-1 do
    FCamList.Add(CaptureDeviceList[i].Name);
  FCount := CaptureDeviceList.Count;
end;

destructor TCameraList.Destroy;
begin
  FCamList.Free;
  inherited;
end;

function TCameraList.GetItems(Index: Integer): TCaptureDevice;
begin
  if (Index < 0) or (Index >= FCount) then
    begin
      result := nil;
      Exit;
    end;
  result := TCaptureDeviceManager.Current.GetDevicesByName(FCamList[Index]);
end;

end.

　
使い方はこんな感じです。フォームには

• Button1 (TButton)
• Button2 (TButton)
• Image1 (TImage)
• CameraComponent1 (TCameraComponent)

が貼ってあります。

unit Unit1;

interface

uses
  System.SysUtils, System.Types, System.UITypes, System.Rtti, System.Classes,
  System.Variants, FMX.Types, FMX.Controls, FMX.Forms, FMX.Dialogs,
  FMX.StdCtrls, FMX.Media, FMX.Objects, FMX.ListBox, FMX.CameraComponentEx;

type
  TForm1 = class(TForm)
    Image1: TImage;
    Button1: TButton;
    Button2: TButton;
    CameraComponent1: TCameraComponent;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure VideoCamera_SampleBufferSync;
    procedure CameraComponent1SampleBufferReady(Sender: TObject;
      const ATime: Int64);
  private
    { private 宣言 }
    FCurrentIndex: Integer;
    CameraList: TCameraList;
  public
    { public 宣言 }
  end;

var
  Form1: TForm1;

implementation

{$R *.fmx}

procedure TForm1.FormCreate(Sender: TObject);
// フォーム作成時
begin
  FCurrentIndex := -1;
  CameraList := TCameraList.Create;
  // カメラがあればインデックスを 0 に
  if CameraList.Count > 0 then
    FCurrentIndex := 0;
end;

procedure TForm1.FormDestroy(Sender: TObject);
// フォーム破棄時
begin
  if CameraComponent1.Active then
    CameraComponent1.Active := False;
  CameraList.Free;
end;

procedure TForm1.Button1Click(Sender: TObject);
// ボタン 1 押下処理
begin
  // カメラの有効 / 無効の切り替え
  if CameraList.Count = 0 then
    Exit;
  CameraComponent1.Active := not CameraComponent1.Active;
end;

procedure TForm1.Button2Click(Sender: TObject);
// ボタン 2 押下処理
var
  IsActive: Boolean;
begin
  if CameraList.Count = 0 then
    Exit;
  // カメラの切り替え (トグル)
  IsActive := CameraComponent1.Active;
  CameraComponent1.Active := False;
  Inc(FCurrentIndex);
  FCurrentIndex := FCurrentIndex mod CameraList.Count;
  CameraComponent1.CameraDevice := CameraList.Items[FCurrentIndex];
  if IsActive then
    CameraComponent1.Active := True;
end;

procedure TForm1.CameraComponent1SampleBufferReady(Sender: TObject;
  const ATime: Int64);
// カメラ画像の取得
begin
  TThread.Synchronize(TThread.CurrentThread, VideoCamera_SampleBufferSync);
end;

procedure TForm1.VideoCamera_SampleBufferSync;
// カメラ画像の取得
begin
  CameraComponent1.SampleBufferToBitmap(Image1.Bitmap, True);
end;
end.

　
理屈上は OS X でも動作するハズですが、動作確認できる環境を持っていないので Windows 用としておきます。

See Also:
[TCameraComponent (FireMonkey Tips)]
http://ht-deko.minim.ne.jp/techf001_additional.html#TCameraComponent