The class I'm TAing has about 60 students in it; I see 40 or so regularly because one of the recitations is early in the morning and fewer people show up to it. Despite being rather lazy about reviewing, I can match around 90% of the photos to names, and make almost no mistakes going in the other direction (trying to imagine the photo given the name).

However, I think I only have around 50% success rate when faced with actual students. The photos I have are likely outdated (they're the photos taken for university IDs freshman year, and I suspect most of my students aren't freshmen) so that might be the problem. Another problem is that when learning the cards, I tend to remember facial expressions and incidental details like background color, even though I try not to; obviously this knowledge doesn't help in actual interaction with the students.

(I used Anki instead of MemStash.co because I couldn't get the latter to do what I wanted.)