смотри клас TStream

из Хелпа BC++

The following example copies the data in the Notes field of Table1 to the Remarks field of Table2.

void __fastcall TForm1::Button1Click(TObject *Sender)

{
TBlobStream *Stream1, *Stream2;

Stream1 = new TBlobStream(Table1Notes, bmRead);
try
{
Table2->Edit();
// here’s another way to create a blob stream
Stream2 = Table2->CreateBlobStream(Table2->FieldByName("Remarks"), bmReadWrite);
try
{
Stream2->CopyFrom(Stream1, Stream1->Size);
Table2->Post();
}
__finally
{
delete Stream2;
}
}

__finally
{
delete Stream1;
}
}