Renames all the files in the current folder based on the Exif date of that image. You’ll need the ‘jhead’ command tool – use apt-get to install it.

for i in *; do mv i "(jhead i | grep date | sed 's/^File date[^:]\+: \(.\+\):\(.\+\):\(.\+\) .*/\1-\2-\3/') $i"; done