First, I know sounds stupid, maybe I’m too confued 
1st line can output picture to pdf, 2nd line can’t.
If I text print out 2nd line to pdf, I can see $cell_datay_picture[$NM_ind] is same as what I declare manually in 1st line.
I know 1st and 2nd line must be different, but I don’t knod how to debug further, I just text ouput and see same.
$url = “http://path-to-picure”;
$url = $cell_detay_picture[$NM_ind];
$pdf->Image($url,4,$y,15,15);