i haven't received any pictures, but my guess would be somewhere in Code: /home/user/.purple/logs/facebook/<username>/ ... The plugin Telegram stores its pictures in Code: /home/user/.purple/telegram-purple/ ...
/home/user/.purple/logs/facebook/<username>/ ...
/home/user/.purple/telegram-purple/ ...
mkdir /home/user/MyDocs/Pidgin_pics ln -s /home/user/.purple/logs/facebook/username/ /home/user/MyDocs/Pidgin_pics