Okay, so this is one of my POCs I was doing recently where I need to convert an image to PDF. I can't disclose the full use case but hope it will help some.
So here is the solution in two simple steps :
1) First insert these three static resources (with the same names)
2) Visualforce Page
(As it was just a POC so code is not clean yet, hope you can take care of that)
Okay so now all set to go, just hit the page and select any image you want to get converted in PDF. Multiple images can also be uploaded.