I am always on the look for new royal wallpapers for either my telephone or computer. Of course I can use my own photos, but there are some real good ones online. For my desktop I use Yellow.bt, which is unfortunately not releasing a royal calendar anymore each month.
For my phone I discovered the lovely designs of the Tsarskoe Selo State Museum & Heritage Site in Russia, that nearly monthly comes with new phone wallpapers. I follow them on Twitter, and in the early days of a month they usually give a link to several designs that you can choose from, showing both interiors and garden pictures of the palace, fitting even to the time of the year. The page where you can download them is in Russian unfortunately. But all you have to do is click on a picture (which includes a calendar for the month in Russian), and choose the download button to download it to your phone.
If you know of any other sites offering this kind of service: let me know.