The key thing is going to be to rely on the numbering of photos in your camera.  The camera should shoot sequentially so you can match it up with sequential cards you give out.  If you don't want to manually handle distribution, you can put a random code on the cards, but still give them an internal order.  You could then tie it to a series of web galleries that are password protected with the code.  You would need some basic scripting knowledge though as you'd probably have to write a custom setup to import the codes in to the gallery application.

Workflow for managing, organizing and sharing a large number of "photos of strangers"?
How would I show the following have a bijection. Which is one to one and onto ofcourse.

$\mathbb{Z}\rightarrow \mathbb{N}$

I know I need to find a function. But I do not see the pattern that makes integer go to natural. I already did this problem from natural to integer but now I want to see it done this way.

I have listed some numbers

$,..,-4,-3,-2,-1,0,1,2,3,4,5,6,7,8,9,..$

$1,2,3,4,5,6,7,8,9,10,11,12,13,14,.$
