Romeoegiuliettaeventi I currently use a php created by me (really terrible) which shows me on the tablet the last photo uploaded to the server and the respective QR code for the photo client to download.
Keep in mind, with Files Gallery, there is no dedicated feature to "show the last photo uploaded". You could of course refresh the dir, and the last photo would be at top. There would also be other older photos there, unless you delete the older photos. If the file name of the latest file is always the same, then you could of course just refresh the popup address of this file name, and it will display latest image, as long as images are not set to cache.
I guess I'm saying the above, because I'm not quite sure why you are using Files Gallery. Of course it's useful for browsing files and photos, but it seems like you are just using it to view a single "latest" photo? In which case, if a client came to me and asked me for that, I would also create it standalone like you have done, because I don't quite understand what you are using Files Gallery for here ...
Also, how do you make the QR code?