How do I download an image I have set as wallpaper on a iPad 2 that is no longer on the Ipad (stored within the OS?)

I have a photo that is set as my lock screen image on my old iPad 2 and I want to download it.

There are no photos within the camera roll but it must be stored within the iPad in order for it to be displayed as the lock screen.

The photo is of a loved one who is no longer with us and I had forgotten that I even had this image and thought it was gone forever so it is extremely precious.

I have not tried to play around with the settings as I do not want to accidentally delete or corrupt it but

as I say, it is still being displayed so it must exist somewhere within the OS, maybe in a internal folder that is not normally accessible by a casual user.

Can anyone help?

Many thanks