In a previous post I explained how to Convert an image to PDF with Gimp, but the quality of the picture in the PDF turned out to be rather poor for printing purpose.
So here is an other way, install tiff2pdf.
On Ubuntu for instance :
Then save your image as a tiff image, then use tiff2pdf to convert it to a PDF. For example, for an A4 sized PDF :
For a multiple pages PDF, preprocess your TIFF files with tiffcp