From a practical point of view, I would have to either write the
JPEG code myself, which is way out of my league, or use a library,
libjpeg is included in all Linux distros but yes for Windows/mac it would add a dependency.
It could be a configure option not enabled by default
For scientific work, e.g. image processing, having to use an external library for the conversions would add
a dependency as well for the user.
