I’m curious as to what you mean by “within ptxprint”.
As far as I know, backgrounds (and section header graphics and verse border graphics) are simply .pdf files. There are a very few example files distributed with ptxprint, which is maybe what you’re seeing. They are in the C:\Program Files\PTXprint\ptxprint\PDFassets\border-art
folder and, in my installation, consist of
A5 page border.pdf
A5 page border - no footer.pdf
A5 section head border.pdf
A5 section head border 2 column.pdf
A5 section head border(RTL).pdf
decoration.pdf
Verse number star.pdf
However, there shouldn’t be any reason you can’t navigate to a different folder and choose any other .pdf file.