cgsecurity.org

I've used Photorec several times to recover images from USB sticks and SD cards for myself and other people and I've never had a problem.

I accidentally deleted a picture from my Nexus 4 and although it's not crucial I'd like to get it back.

I've enabled USB debugging but it doesn't show as a drive in Photorec or Testdisk. It shows in Widows explorer but not as a drive. Am I doing something wrong? Does it need to be rooted?

You need to enable the USB mass storage mode on your Nexus 4.
http://www.cgsecurity.org/wiki/PhotoRec_FAQ#Android_4.2

Thanks for that. Unfortunately USB mass storage mode isn't an option on my Nexus. There's only MTP and PTP. A quick search suggests that USB mass storage is only possible on an SD card which the Nexus 4 doesn't have.

Maybe it's just not possible on devices like the 4 and the 10 which I believe also doesn't have an SD card.