dd_rescure, is an an advanced evolution of dd, a command line program that has been ported only for UNIX/Linux; dd_rescure uses a complex series of flags to allow the user to image or write data from and to raw image files. It is a tool more suit that update to you in real time with the status of the operation visualizing some important info.
Here is a common dd_rescue command:
dd_rescue /dev/hda myfile.img
Don't us if= and of= like dd becouse dd_rescure it doesn't work!