If you on Fences 4, and from my observation, Fences do take Snapshots of your desktop daily but I believe its in png file format. And it will be save in "C:\Users\xxxxxx\AppData\Roaming\Stardock\Fences\Backups" So, I can't be sure if your jpg file from Fences. What you can do is disable Fences daily backup snapshot save option and see if the .jpg still appear.

Thank you,
Basj,
Stardock Community Assistant