Greetings and salutations,
I have read the job description and I am willing to provide a solution. Wallpaper changing can, of course, be done programmatically, in almost any language, so if you have any preferences, please do not hesitate to tell me. I would, optimally, write it in C#.
Other than that, I would like to know if you want the application to have GUI or if you would like it to be a command line application that, perhaps, integrates into an existing program.
Please feel free to contact me with the details and I will respond as soon as possible.
Until then,
Best regards.