Personal opinion/experience. If you want strong LoR, the professional and correct way to request (especially from someone several years ago) is to e-mail asking for 10 or 15 minutes of their time in person. Then you meet with them face-to-face and sell yourself for 10-15 minutes (the same way you structured your e-mail) and ask them for a recommendation. Also, it is proper to provide them 6 weeks minimum for their letter.
I'm not saying it has to be done this way, but if I was a a professor that taught you a few years ago, it is possible I wouldn't remember you very well with a photo. They may have taught several hundred students in that time. Example: one of my LoR, I went through this long formal process, and the other two I just knocked on their door and said, hey, remember me? Shoot, the dentist LoR I got, I would text him every couple days to ask where he was in the process of writing my letter.
Again, in my opinion, when choosing who you want to write you letters, you need to read the room. What is your relationship with them and how should you proceed in requesting the letter. I apologize if you read a negative tone in this message as that is not the intention. 😀 Feel free to ask any questions.