An agent posted this article from The Stage on Facebook today and I think it is so good. I'm going to quote a little here, but it is well worth reading the entire article.
The agent relates experiences just like those of actors who have come to see me for their headshots!
“You need to change your headshot” might seem like a cop-out on the part of the agent in response to an actor's complaint that he or she hasn’t had many auditions, but also consider that your headshot must not only be representative of who you are, but that, in a sea of 60,000-plus headshots we want yours to jump off the page because it’s that good: striking, eye-catching. I have personal experience of actors who weren’t getting seen until we discussed new headshots, agreed on the look and then uploaded them to Spotlight only to land an audition the very next day and another one or two in the following week. I’ve also had actors who refused to change their headshots for various reasons, subsequently left the agency and immediately got new headshots (usually at the insistence of the new agent) and then – surprise, surprise – got an audition. Was it really the new agent or was it perhaps that they had finally listened to advice?"