From the reviews:

It also simply duplicates the work of Facebook's Graph Search.

There, so far, is nothing original or creative here, and considering their intrusive, complicated "YOU MUST MAKE YOUR FRIEND JOIN" policy, I cannot endorse this extension.

Steer clear.

This site is free to post to and is largely driven by upvotes from free accounts. There is no inherent moderation (sure there is a lot of vote ring moderation) that would prevent an article from hitting the frontpage.

From what I've briefly seen, it just redirects you from the profile page to this URL: https://www.facebook.com/search/{{fbuid}}/photos-of

where, as you can guess, {{fbuid}} is the id of the user. And yeah, you can view photos from users that you aren't friends with despite that by looking directly at the profile you couldn't view them.

Quick look at the source code from the crx file [1]: Some kind of Facebook graph search using the ID of the targeted user.

[1] Use this to download it, then just unzip: https://chrome.google.com/webstore/detail/give-me-crx/acpimo...

I'm just guessing, but one way you could do it: get some level of access to the FB accounts of all of getpicturebook users. As long as the user whose pictures you want to see is a friend of one of those people, you can now see them.