[[AgustinOrtu]]

Yo empleo esta unit en XE7, me conecto por FireDAC a una BD Firebird 2.5 y el campo en cuestion esta definido asi:

Código SQL [-]
Imagen BLOB SUB_TYPE 0 SEGMENT SIZE 16384

La unit es la siguiente:

Código Delphi [-]
unit Data.Graphics;

{ Todo viene de https://delphihaven.wordpress.com/20...aphic-formats/
  Estas funciones leen el contenido de un BLOB y determinan que tipo de TGraphicClass debe usarse para leer mostrar
  una imagen (JPEG, BMP, etc)
  Gracias !! }

interface

uses
    System.SysUtils, System.Classes, Vcl.Consts, Vcl.Graphics, Vcl.Imaging.GIFImg, Vcl.Imaging.JPEG,
    Vcl.Imaging.PngImage, Data.DB;

const
    MinGraphicSize = 44; // we may test up to & including the 11th longword

function FindGraphicClass(const Buffer; const BufferSize: Int64; out GraphicClass: TGraphicClass): Boolean; overload;
function FindGraphicClass(Stream: TStream; out GraphicClass: TGraphicClass): Boolean; overload;

procedure LoadPictureFromBlobField(Field: TBlobField; Dest: TPicture);

implementation

procedure LoadPictureFromBlobField(Field: TBlobField; Dest: TPicture);
var
    Graphic: TGraphic;
    GraphicClass: TGraphicClass;
    Stream: TMemoryStream;
begin
    Graphic := NIL;
    Stream := TMemoryStream.Create;
    try
        Field.SaveToStream(Stream);
        if Stream.Size = 0 then
        begin
            Dest.Assign(NIL);
            Exit;
        end;
        if not (FindGraphicClass(Stream.Memory^, Stream.Size, GraphicClass)) then
            raise EInvalidGraphic.Create(SInvalidImage);
        Graphic := GraphicClass.Create;
        Stream.Position := 0;
        Graphic.LoadFromStream(Stream);
        Dest.Assign(Graphic);
    finally
        Stream.Free;
        Graphic.Free;
    end;
end;

function FindGraphicClass(const Buffer; const BufferSize: Int64; out GraphicClass: TGraphicClass): Boolean;
var
    LongWords: array [Byte] of LongWord absolute Buffer;
    Words: array [Byte] of Word absolute Buffer;
begin
    GraphicClass := NIL;
    Result := False;
    if BufferSize < MinGraphicSize then
        Exit;
    case Words[0] of
        $4D42: GraphicClass := TBitmap;
        $D8FF: GraphicClass := TJPEGImage;
        $4949:
            if Words[1] = $002A then
                GraphicClass := TWicImage; // i.e., TIFF
        $4D4D:
            if Words[1] = $2A00 then
                GraphicClass := TWicImage; // i.e., TIFF
    else
        if Int64(Buffer) = $A1A0A0D474E5089 then
            GraphicClass := TPNGImage
        else if LongWords[0] = $9AC6CDD7 then
            GraphicClass := TMetafile
        else if (LongWords[0] = 1) and (LongWords[10] = $464D4520) then
            GraphicClass := TMetafile
        else if StrLComp(PAnsiChar(@Buffer), 'GIF', 3) = 0 then
            GraphicClass := TGIFImage
        else if Words[1] = 1 then
            GraphicClass := TIcon;
    end;
    Result := GraphicClass <> NIL;
end;

function FindGraphicClass(Stream: TStream; out GraphicClass: TGraphicClass): Boolean;
var
    Buffer: PByte;
    CurPos: Int64;
    BytesRead: Integer;
begin
    if Stream is TCustomMemoryStream then
    begin
        Buffer := TCustomMemoryStream(Stream).Memory;
        CurPos := Stream.Position;
        Inc(Buffer, CurPos);
        Result := FindGraphicClass(Buffer^, Stream.Size - CurPos, GraphicClass);
        Exit;
    end;
    GetMem(Buffer, MinGraphicSize);
    try
        BytesRead := Stream.Read(Buffer^, MinGraphicSize);
        Stream.Seek( - BytesRead, soCurrent);
        Result := FindGraphicClass(Buffer^, BytesRead, GraphicClass);
    finally
        FreeMem(Buffer);
    end;
end;

end.

Ejemplo de uso:

Código Delphi [-]
var
  Image1: TImage;
begin
  LoadPictureFromBlobField(TBlobField(DataSet.FieldByName('CampoBlob')), Image1.Picture);
end;

Con esto podes cargar indistintamente un bmp, jpg, jpeg, gif, ico o png