In one of my projects, I tested and / or implemented probably six or seven different ways of moving from an image to a PDF over the past six months. I ended up returning to ReportLab (which I initially avoided for reasons similar to the ones you described), because everyone else (for example, the inability to set document metadata).
ReportLab is not as difficult to process as it seems at first glance, and it can save you a lot of refactoring, loaded with a headache later. I strongly recommend that you go ahead and use it and therefore know that if you ever want to do more, you will have the opportunity too, and not do what I did, and bounce between different utilities, libraries, and formats .
EDIT:
, Platypus, ReportLab, , , .