Bing Desktop local image folder

Just found it this morning:

C:\Users\USER\AppData\Local\Microsoft\BingDesktop\en-US\Apps\Wallpaper_5386c77076d04cf9a8b5d619b4cba48e\VersionIndependent\images

Bing Desktop 1.3.328.0 on 12/07/17

C:\Users\{User}\AppData\Local\Microsoft\BingDesktop\themes

Looks like only the last 8 are there, maybe they are being pruned.