img2pdf is a small application which converts a list of images to a single, multi-page PDF document.
It was designed specifically to convert scanned pages to PDF format, but it will accept images of any aspect ratio and scale them to full page size (which, in general, will not maintain the aspect ratio).
The hard work is performed by the Panda PDF library and its dependencies.
Panda is a prerequisite; requires libpng, libtiff, and libjpeg in order to support the corresponding image formats, and libpng requires zlib.
Once they're compiled and installed, edit the Makefile to point at their locations (and to specify your compiler if it isn't GNU C), then simply: