Consider looking at headshots day-in, day-out. You probably will never have to do it, but as a developer, I do. Headshot photographers do it too, but most importantly, so do Casting Directors. When you look at that much data, you can spot the difference between a good headshot and a bad one. Here are three most important mistakes:
Not interesting enough:
If you look like 1000 other people with no distinction between your headshot and 100 previous ones, it just isn't standing out in any way. You need to break through the noise. After all, if it does not meet this qualification then it doesn’t get seen. A great photographer who specializes in headshots will know tricks to make you stand out. Listen to their advice. If you are looking for a headshot photographer, don't forget to check out https://www.headshotlist.com - but I digress. Photographers will use proper lighting, contrast and composition to capture your spirit.
Some actors DO stand out, but not for the right reasons. If your headshot does not look to be of a professional quality, you won't even make it to the consideration pile. That means... don't send in a selfie. Seriously. If you're applying to a smaller production and you are going up against two or three other actors, perhaps they'll call you all in anyway and your headshot won't matter. But if you're going up against 100s of other actors, that headshot WILL get you disqualified unless the Casting Director knows you personally and would vouch for you. My guess is that it's not the case, so please, do keep that in mind.
Your headshot HAS TO look like you. I've seen a lot of actor headshots, and then I met these actors in person... Let me tell ya, Photoshop can do a lot, but you don't want your headshot to misrepresent you. If the Casting Director doesn't know you (which is probably most of the time), and you get called in from a headshot, and you look nothing like it... What are you actually expecting to get out of this? Casting Directors are trying to find the right person for the role. Your headshot catches their eye, they bring you in and expect the person in that headshot to walk in the door and there you are. Maybe you are no longer blonde, or maybe you shaved your beard, or perhaps your real wrinkles have been photoshopped off of your face. You can't expect them to treat you seriously going forward, they will be distracted that they've been duped.