Recover Fat32 files from a usb hd overwritten with a Freebsd image

[Victor]

I'm risking to be hanged by the neck by my daughter!
Well the fact is simple and dramatic. My daughter had a usb external hd, formatted as Fat32 filesystem,  where she was keping all her jpeg photos. 
Accidentally I used this same usb drive to copy the FreeBSD-11.2-RELEASE-amd64-memstick.img using the classical

sudo dd if=FreeBSD-12.0-RELEASE-amd64-memstick.img of=/dev/da0 bs=1m

At the end of the process I became aware of the terrible mistake and I've never used the usb hd to start Freebsd.
I wonder if I can try to recover the jpeg files from the 'extinct' fat32 filesystem. Surfing the net I found many solutions and I'm somewhat confused (photorec?).

In order to avoid the hanging, is there anyone of you experts able to give me a useful hint for this specific case?
Ciao
Vittorio