I took a look at this, and it’s not such a simple task for beginners because of the complexity of the libjpeg API. However, I put together a start at:
which at least deals with the initial task of wrapping the jpeglib.h header file and mirroring all of the data structures (with help from Clang.jl). As explained in the README, it is now possible to use the library to read a JPEG header and call the low-level API functions directly.
If someone is interested in building on this to put together a higher-level Julia API, let me know.
Update: looks like this package by @ianshmean also provides low-level wrappers for libjpeg, and is a bit farther along: GitHub - IanButterworth/ImageIODevelopment.jl: Developing better IO for images in Julia via libpng, libjpeg, libtiff etc.