Solution
Add the image to the file cabinet which you need to add to PDF
Open the Image as a file in Netsuite as below

Copy the 3rd URL and paste in the PDF template in a img src tag
<img src="https://386782-sb2.app.netsuite.com/core/media/media.nl?id=655728&c=386782_SB2&h=pJ1Gen3ngqn5E5dgz_pDtRs5L37Lnfyd19Y0plLBy9gEhupl "/>Note: After &, add amp; in the URL. Other the image will not be shown in PDF