Oh. I see now that you've modified jpeg_metadata_parser.js to rely on jpeg.js.  That seems like a heavyweight dependency to add: to replace 350 lines of code with 3200 lines of code with no change in camera features.  

I think it would be better to leave jpeg_metadata_parser as it stands as a lightweight EXIF parser for image size, thumbnail and orientation.  Then you can load your full-featured jpeg.js library only when it is needed to read and rewrite the entire EXIF segment.