Can I download a users FB photos to match information to them?

Question

I've been scouring the internet but haven't been able to find a good answer.

THE SCENARIO

I'm in the midst of checking policies for an app where if I take a photo (using an iphone, android, anything...) of a FB friend (who I'm currently standing in front of), I can find out my FB friends name and other helpful information to lead a conversation.

(In other words, help me remember a friends name who I've forgotten who i currently have as a facebook friend).

WHY

I'd rather not run into any privacy or data issues and figure if this is doable before I spend a bit of time and money developing such an app.

I know google prohibits this...

HOW FB WOULD BE INTEGRATED

I'd develop my own or use another facial recognition API to do the actual comparing of my friends photos to the photo I just took. That being said I imagine that the app would download a couple photos my friends have been tagged in, in order to compare the photo I just took to the ones that I've found on facebook.

MY ASK

Could you point me to where I can find the policy where it states that I CAN or CANNOT do this?

JUST TO BE CLEAR

I'm only comparing and pulling up information for the photo I just took to photos of friends that have been found on FB that I would already have access to.

Thanks for the feedback in advance. This community is awesome and I'm glad to be apart of it.

Long live curiosity.

Pascal