This thread is bit lol-ish. The OP asked a very simple question: is it possible to upload an already existing picture via the feedback app.
So this has NOTHING to do with the Insider Hub (which is temporarily available on the last builds) and does certainly NOT require a hard reset.
The answer is : no, it's not possible. You can only use two means :
a) when in the app you're "testing", use the hotkey "Power+vol down" to trigger the feedback app. This will include a snapshot in your report,
b) when reporting, press the camera icon on the bottom part to be able to snap as many screenshots as you want.
That's it. Not possible to upload from photo gallery for instance.
I hope it answers your question Snowy Nokia.