I don't think it's possible to insert images into notes/comments. I've searched through the manual of Foxit Reader, but there was nothing related to this operation, therefore I believe it's not possible.
The Reader allows you to insert images directly into the PDF documents, not on specific items already contained in the PDF file. I believe that you will need a PDF authoring tool that has additional functions to be able to customize the items from a PDF entirely.
I recommend checking the Adobe Acrobat Pro DC: https://acrobat.adobe.com/us/en/acrobat/acrobat-pro.html