I need to take a screenshot and send it via post to a web service. I think for the post part i will use liburl.
Can this be accomplished completely cross platform and without having the need for the final user to install additional libraries/software?
You could also use PyQt5 for this:
There is not anything in the standard library that can do this for you. Theoretically, you might do it yourself by making os-dependent system calls with ctypes but that seems like a lot of unnecessary work to me. Here is a working script to make a screenshot using wxPython: