Judging only by the screenshots of the app in the iOS app store, and not by downloading it and using it myself:

* It appears you get 100 points for a shelfie.

* According to the listed rewards, it takes 10,000 points for a $5 walmart gift card

* Thus, you'll need to take 100 shelfies for $5.

My assumption is that different products / stores will award different point amounts so it will probably just depend.