A proof of concept Windows FS minifilter driver that dynamically blocks osu! map backgrounds from loading on the fly.
Note that this requires TESTSIGNING to be enabled in order to load the driver, which is incompatible with osu! score submission, and the anti-cheats of many games for as long as TESTSIGNING is enabled. (ie, Vanguard, BE, EAC all refuse to launch)
You can technically use kdmapper or an EFI based mapper with Secure Boot disabled, but I heavily don't recommend doing this. This is just a POC when playing offline (and in which case it's much easier to just patch the game directly)
Once the driver has been loaded, it will listen to all file handle opens and find any from a process named osu!.exe,
and if the file is inside the Songs folder while being a JPG or PNG, it blocks access to the file.
The advantage of this is that you do not need to alter any map files, or do mass file renames every single time you want to disable backgrounds, which is error-prone and very slow with thousands of maps.