The lumbar support isn't actually supposed to support your lumbar. It's meant to support the back of your pelvis. The correct sitting position is slightly forward, 5-10 degrees without curving the back forward. Your shoulders aren't supposed to rest on the chair unless you're leaning back and resting (not working with the mouse and keyboard). I've had my share of ergonomics classes. The illustration is incorrect, because the back is resting on the lumbar support, which forces the shoulders to be in an active position and forces the neck forward. This also forces the arms into an unnatural lifted position, though they should be resting on your sides at 90 degrees. Though that has more to do with the table being too high. Also, raising the monitor a little would be beneficial.

Though the "correct" posture on the picture isn't as bad as the incorrect one. That one's way, way, way worse.

That said, my comment was meant to be humorous.

I will refer anyone who wants a better recap to this actual ergonomist.