function CheckJPG(Path: String): boolean;
var
    C: Cardinal;
    AStream: TFileStream;              //здесь всё ок
    IsCorrect: Boolean;
begin
    IsCorrect := True;
    Astream := TFileStream.Create(Path, fmOpenRead);
    C := 0;
    Astream.Position := 0;
    Astream.ReadBuffer(C, 3);
    if C = $FFD8FF then
        IsCorrect := True
    else
        IsCorrect := False;
    Astream.Destroy;
    CheckJPG := IsCorrect;
end;



function CheckPNG(Path: String): boolean;
var
    C: Cardinal;
    AStream: TFileStream;
    IsCorrect: Boolean;        //здесь не ок
begin
    IsCorrect := True;
    Astream := TFileStream.Create(Path, fmOpenRead);
    C := 0;
    Astream.Position := 0;
    Astream.ReadBuffer(C, 8);
    if C = $89504E470D0A1A0A then
        IsCorrect := True
    else
        IsCorrect := False;
    Astream.Destroy;
    CheckPNG := IsCorrect;
end;