Reference images for expressions?
Expressions is a thing I enjoy doing, but not having any artistic background, I often lack a clear idea of how to achieve what I'm aiming for, or even a clear idea of what the final result would look like. I tend to fiddle with the controls, and trying things quite hapzardly. "Let's see if it will be closer to what I want if I raise the exterior of the eyebrows? Hmmm...no...what about lowering them? Wrinkling the nose? Adding some "sadness"? Raising the upper lip?" . I sometimes google, say, "awe", and look if I can find some photo with the kind of expression I want and what the various elements of the face look like, but on the overall it's not very efficient.
So, I'm wondering if there are "expression libraries" out there, or something like that, where I could find photos of a large range of expressions to use as references.

Comments
Google, pinterest...
How about a mirror? Artists have been using them for hundreds of years. Or if you see an interesting expression while watching a movie, hit the 'Pause' button.
3DSK is a good source - paid, but good too
You can pick up Mark Simon's book Facial Expressions-A Visual reference for Artists for around $12 on Amazon and there's also a kindle version. For pre-built libraries, I've found SimonWM's Expresions and Face Aniblock series to be an excellent base to begin with as they cover all the DAZ figures since V4m, the parameter dial versions all have clear thumbnails for each expression, and the aniblock versions let you see what it looks like in real-time animation.
Ouch... just under $27.00 CDN. That's a lot more than exchange... I hate getting <expletive deleted> on book prices up here. Sigh.
Yeah, but your healthcare costs put ours to shame and you have Tim Horton's, Aero bars and ketchup chips, so it kinda balances out.
It takes me over a month to get a Dr.s appt, so most people just go to emergency - you don't even want to know about your chances of getting to a specialist when needed. I'm still boycotting Tim Horton's, and I don't eat junk food. ;-P
I'd rather have books :-)
There are actually some very nice resources for free available over on DeviantArt. You need to look under Resources and Stock Images > Stock Images > Model. You can further select by male or female etc.. A lot are poses, but many include useful expressions as well. I don't know whether you are looking for male or female, but if the latter it is worthwhile looking at Faestock's portfolio, as one good example - she has lots of expressions - Jessica has a very expressive face.