First off, you don't want a Service - they are designed to operate without any GUI and wouldn't normally be expected to access the desktop. Indeed, you have to specifically allow a service to access the desktop by checking the "Allow service to interact with Desktop" option, but there is no guarantee that there will be a desktop for it to interact with as services can run unattended.
A better way to get rid of the console window is to call it a winforms app, but remove the line
Application.Run(new MyForm());
from the Main function (in the program.cs file).
I haven't tried this myself, but I think you would need to use
Process.GetProcesses Method (System.Diagnostics) | Microsoft Learn[
^] to identify the process behind the Photos app, then use that to access the main window handle - you have then send it messages to location at a specific point on screen.