An AutoHotkey v2 script for Windows 10 that advances a wallpaper slideshow to the next background. This automates right-clicking the desktop and selecting "Next desktop background" from the context menu.

nextwallpaper.ahk

; This script advances the wallpaper slideshow to the next image. Requires AutoHotkey v2.
; Author: Mike "ZiRC" K. (https://github.com/zlrc)
; License: CC0 (https://creativecommons.org/publicdomain/zero/1.0/)
; 
; Relevant AutoHotkey Documentation:
; - ComObject: https://www.autohotkey.com/docs/v2/lib/ComObject.htm
; - ComValue: https://www.autohotkey.com/docs/v2/lib/ComValue.htm
; - ComCall: https://www.autohotkey.com/docs/v2/lib/ComCall.htm
; - DllCall: https://www.autohotkey.com/docs/v2/lib/DllCall.htm

Sleep 2500

; 1 in `numImages` chance the rest of this script doesn't get executed.
numImages := 6
if Random(1, numImages) == 1
    ExitApp


; The code below is an updated version of a snippet written for AHKv1, documented here: https://www.autohotkey.com/boards/viewtopic.php?style=7&t=34436#p242537
try if ((pDesktopWallpaper := ComObject("{C2CF3110-460E-4fc1-B9D0-8A1C0C9CC4BD}", "{B92B56A9-8B55-4E14-9A89-0199BBB6F93B}"))) {    
    ; HRESULT AdvanceSlideshow(monitorID, direction) -
    ;     https://learn.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-idesktopwallpaper-advanceslideshow
    ; `monitorID` is a pointer to the target monitor's ID. Setting to `NULL` targets the monitor that is scheduled to change next.
    ;     (below, passing `0` as the pointer value is the same as passing `NULL` to the function.)
    ; `direction` indicates which direction the slideshow advances (0 is forward, 1 is backward).
    ; NOTE: It looks like Windows API has yet to support going backwards, which means that setting `direction` to 1 will return a "Not Implemented" error.
    ComCall(16, pDesktopWallpaper, "Ptr", 0, "UInt", 0) ; IDesktopWallpaper::AdvanceSlideshow(NULL, 0)

    ; `16` above refers to index 16 of the virtual method table for IDesktopWallpaper (i.e. the 17th method declared for this interface).
    ;     - A reference for IDesktopWallpaper's virtual table can be found here: https://github.com/retep998/winapi-rs/blob/5b1829956ef645f3c2f8236ba18bb198ca4c2468/src/um/shobjidl_core.rs#L292
    ;     - Indices start at 0, so the "17th" method is at index 16.
    ;     - IDesktopWallpaper inherits IUnknown, which declares 3 methods that occupy the first 3 indices (0, 1, and 2).
    ;     - This means that, when counting the indices for IDesktopWallpaper methods, start at index 3 (which refers to `SetWallpaper`).
} catch {
    MsgBox "Error: " . A_LastError
}