Below are the thoughts of a prominent casting director on headshots. She has worked at the National Theatre, The Gate, The Open Air Theatre and The Southwark Playhouse so knows a thing or two. She also moonlights for MI5.
I look for two main things in a headshot: firstly, it should be representative of the way you usually look on a day to day basis (albeit a good day...). For example, if you don’t wear any make up usually, don’t wear loads on the day of the photo shoot, or if you have lots of facial piercings, it’s a good idea to show this in at least one of your portfolio photos to avoid surprises.
The second is that a headshot should also show me roughly how old you are, and because of this they do need to be updated every so often. When someone comes into a meeting and they look 10 years older than their photo, it’s disappointing. Not only does it waste the director’s time, but also mine and yours, and on many projects time is not something we have much of for the casting process! Don’t be scared of looking old, it might just be I’m searching for someone who looks your age.