I disagree very strongly with the principle that services should be purchased with a photo. I will share a personal experience.
Traveling from Luxembourg to Brussels by train I made an arrangement for a room via AirBnB. It being the first time, they asked me for ID, and Credit Card information. I provided that. By the time I got off the train I received a response from AirBnB that my reservation had been canceled due to the fact that I hadn't provided a photo of myself for AirBnb. I believe the reason was because they wanted to know that I was a "real person", but the exact phrasing escapes me. This was not the case since I provided a photo of my driver's license as my ID. As a result I had to scramble to find a room in one of the most expensive cities in the world for this at the last moment (which was expensive).
I strongly disagree with the idea that "your face" should be integrated with a purchase. I strongly agree that your identity which includes but should not be limited to a subset of "your face" should.
If you are proceeding down this path I recommend having a user select a photo, rather than taking a self portrait.
My argument for tipping:
Make somebody who is working feel special if they are making you feel special.
Disclosures:
I worked in the service industry for years while also holding an engineering internship and getting a EE degree. There were many people who were not my regulars that made me feel special on days where there wasn't much else to.