Hands Figure in to Portraiture

I may not be doing many hands in my first portrait studies but I do know they will be an important element to know how to paint when I start portraits at three quarter length and full length. To start though I will concentrate on head and shoulders first.

Today I was going to draw a Rembrandt head study but this hand caught my eye and I realized practicing hands will be equally important to study.

Here is a copy I've attempted, can you guess the painting it's from?