The screenshot feature can be pre-programmed to save your screenshots to any location automatically.
To program, Click "screenshot" and click "options." Then select "other locations". You can then select ANY location that appears on your Finder list. In your case you would select Pictures.
Now, every time you click screenshot, without doing anything, your screenshot will be saved in Pictures or any other Finder location automatically.
Now all you need is a shortcut to invoke the screenshot feature since screenshot itself is now programmed to do a full screen capture directly to your pictures location.
I do a LOT of screenshots and they are automatically saved to my NAS. I don't really need a shortcut. I just click the screenshot Icon, another click to capture and the rest is automatic.
I have screenshot programmed so that all of my screenshots are automatically saved to a folder on my NAS. Basically just 2 clicks. I hope this helps.