An earlier post How to handle figures and images using MikTeX Plain TeX (not LaTeX) on a 35 year old document (that I am not allowed to comment on) suggested this simple solution. (I also am working on converting a thesis from the 1980s.)
\pdfximage width .25\hsize{man.png}
\pdfrefximage\pdflastximage
which worked immediately for me using the pdftex command. Thank you!
However, the image is not centered on the page but up against the left margin. Does anyone know how to center the image?
miniltx
that can be used within plain TeX to incorporate graphics. I remember using it in the past to do the sort of thing you're trying to do. Unfortunately,miniltx
on CTAN comes without user documentation, and I no longer have access to projects I worked on before I retired. But since what you have might be treated as a box, you might try to pack it in a\centerline
.