script/program to combine images to make PDF?

Hey all,
I'm writing up some scripts (combination of bash, Python) to run some tests, collect some data and create some images. Is there anyway to write a script (or a something in /usr/bin) to combine these images into a PDF?

I know you can do this with Adobe Acrobat Pro and Automator but I would much prefer just having it done in the script automatically.

Many thanks!