We often get asked, if there's a simple way to join PDFs from many images under linux. The task is very trivial, if you have 1-2 images, as you can use many of the graphical applications. If you have 10-20 or more, we recommend pdfjoin. It runs under Linux on a command line and allows for a quick images to PDF combine.
Under Ubuntu, it is part of the texlive-extra-utils package.
To install the package, run the following:
apt-get install texlive-extra-utils
To combine the images, you can run something like this:
pdfjoin --letterpaper --fitpaper false --rotateoversize false *.jpg --outfile combine.pdf
This is assuming your images are names something like 01.jog, 02.jpg, etc.
If you want them in a particular order, you will have to run something like this:
pdfjoin --letterpaper --fitpaper false --rotateoversize false 01.jpg 03.jpg 02.jpg 04.jpg --outfile combine.pdf
The result will be in combine.pdf