if  OpenPictureDialog.Execute then
begin
   img1.Picture.LoadFromFile(OpenPictureDialog.FileName);
   btnPicture.Text:=OpenPictureDialog.FileName;
end;

var
Stream:TMemoryStream;
Stream := TMemoryStream.Create; // 创建内存流
// 将图片保存到内存流中
img1.Picture.Graphic.SaveToStream(Stream);
ParamByName('picture').LoadFromStream(Stream,ftBlob);
ParamByName('IsSavePicture').Value:='1';
Stream.Free;  //用完了马上Free掉

var

Stream:TMemoryStream;
Jpg:TjpegImage;

if fieldbyname('IsSavePicture').Value='1' then
begin
 Stream:=TMemoryStream.Create ;
 Jpg:=TjpegImage.Create ;
 TBlobField(FieldByName('picture')).SaveToStream(Stream);  // 显示的转换为BlobField并保存到内存流
 Stream.Position :=0;
 jpg.LoadFromStream(Stream);  // 加载图片
 img1.Picture.Assign(Jpg);
 Stream.Free;
 Jpg.Free;
end
else
begin
 img1.Picture :=nil;