Attached Link: http://freeimage.sourceforge.net/

> Quote - Don't render to JPEG format

Good advice due to JPEG being a lossy format.
At the very least you'd want to set the quality to 100 rather than leaving it at the default.

Quote - I've no idea which toolkit the Poser developers used to support JPEG but I'm guessing it wasn't the most expensive one.

It didn't cost them anything, see attached link.
The library makes use of several other open source libraries for reading and writing well known image formats (JPEG, PNG, TIFF, EXR) which are used by many other pieces of software for the same purpose.