16GB is a huge chunk to go missing.
I would open an xterm, do a du -h -T and see how much of your 32GB is left. My gess is you will see that 16G of it is still assigned somewhere.

You might want to do the following to try to find any JPG files. This may give you a hint at where your files are.

sudo gainroot
# find / -name "*.[Jj][Pp][Gg]" -print

This will search your entire file system for any jpg file and hopefully point you at the location of where they are.