Why a headshot
Your headshot is effectively your primary branding tool.
Casting agents seek a specific look that fits their mental image of a particular character they are casting. Use that to your advantage. The primary requirement is that you must look like your headshot! Sounds obvious, but if you arrive at a casting and your headshots have been retouched to iron out those wrinkles, you will look nothing like your headshot and have immediately ruled yourself out!
A lot of care is taken with the lighting to ensure that in post production only the subtlest adjustments - skin tone, colour balance need be employed so the final images represent you, but on a good day! Your headshot is not a beautiful portrait, but shows a true representation of you. It is effectively your brand. Of course, with appropriate direction I am also helping you to provide "depth" so that your character is captured too - I am not a fan of the "deer in the headlights" look!
You may have features that you dislike, perhaps the shape of your nose, or protruding ears. Far from being an embarrassment, I suggest you need to “own” those features; they may be exactly what the casting director has in mind for a specific character. The headshot needs to celebrate those unique features that make up your unique "brand".
A casting agent assesses a huge number of images, so it is essential that your headshot stands out from the rest. Your headshot can’t get you a part, only your acting can achieve that, but it can get you an audition. If you can get that audition, then the quality of your acting will be the deciding factor.
Pointers to prepare for your headshot