@Playful
PicViewer is an incomplete work. It's more of a proof of concept, than a final solution. It considers jpg/jpeg file to be the whole document.
There is another solution. You can zip your jpg files. Then, instead with PicViewer, they will be opened with PDFReader (PicViewer and PDFReader are components of KPV/Librerator). You can use pg_fwd/pg_bck to go to next/previous picture inside the archive. And the rendering of jpg images is better. That's how I read manga on my K3.
When inside zip archive, KPV/Librerator will show png and gif files too. Only jpg/jpeg are shown with PicViewer.
I hope this helps.
Regards,
Kai