The data comes via the free and public work from the collaborators at the unitedstates github repo:
https://github.com/unitedstates/congress-legislators
It's also worth referring to the Sunlight Foundation's writeup:
https://sunlightlabs.github.io/congress/index.html#legislator-spreadsheet
Here's another repo from the unitedstates folks:
https://github.com/unitedstates/images#using-the-photos
It's kind of nice that given a Congressmember's bioguide_id, you can get their official mugshot:
https://theunitedstates.io/images/congress/[size]/[bioguide].jpg
e.g.
https://theunitedstates.io/images/congress/225x275/C000174.jpg
