LabVIEW
Counting a stack of card.
A stack of cards has 52 cards+ 2 Jokers. No need for Vision!
Just kidding. Sounds like fun.
What are the conditions? Can you pick the background? The lightning? The scaling\distance? Should it work for any deck of cards or just one? Is this BW or color? Should it work for the fronts, the backs or both (or mixed)? Can the cards overlap (that could make it near impossible to detect)?
You'd probably want some contour detecting, and then some analyzing of these contours. Of course after proper conditioning of the image, probably at least (local) thresholding. It's a lot like marker detecting in OpenCV.
If you have images, posting them might help.
Search LabVIEW like a graph! 
The thing is, this might not be feasible.
Vision is tricky, and often needs a lot of creativity.
Is counting the cards the goal, or is using vision a requirement? I'd say simply weighting the cards should work pretty good.
Using vision, again there are tons of questions. Most of the questions from my earlier post still apply.
Intuitivelly, I feel you'd get a good estimate at best if the cards are stacked and counted based on the height of the stack. But again, the trick is to cheat (be creative) to the extend of what's exeptable. And we don't know what is.
I've done a 'measure length by vision'-program once, but it's at best a decent estimate (which in this case was good enough since it replaced manual measuring against a template).
For a more correct value the suggestion to weigh is a lot better.
/Y
I guess one could build a system (camera\lens\lightning) in a way the actual transitions between the cards are visible. It would require a high resolution, specific lenses, and that might limit the maximum nr. of cards.
With a setup like that, the software would be fairly easy.
To suggest a software algorithm\method, we'd need at least a few images of any\all the situations that are to be supported. So with a rigid setup (fixed lightning, distance, angles, etc.), we'd 'only' need a few images of: different number of cards, different colors, different thickness, and so on. That might mean a few hundred to several thousand images.
