/home/user/.gnome2/nautilus-script
create files:
"Rotate CW"
"Rotate CCW"
"Rotate 180"
edit these in gedit, and than make them executable.
This is the script for Rotate CW:
#!/bin/bash
mogrify -rotate 90 $NAUTILUS_SCRIPT_SELECTED_FILE_PATHS
for CCW use 270 and for 180 use 180 instead of 90.