I have used Photorec in the past. You will have to install (if it is not already installed) testdisk
Photorec is part of the Testdisk package.
To run Photorec on an image file, do:
sudo photorec <imagefilename>
To recover image files run (substitute drive name):
sudo recoverjpeg /dev/sda1
Recovered files will be saved in your home directory, with names following the pattern image*.jpg.