How to get a good headshot
A head shot is the most important picture you will ever take as an actor, this is the first picture a casting director will see so it needs to be eye catching.
A casting director can shift through 1000's of applications a day without even looking at people's CV's or show reels, this can be a case of you not looking right for the part or the head shot not sticking out. A head shot needs to stick out as a thumbnail as this is how a casting director will go through online applications.
when choosing a head shot out of 100's taken, all you want is a touch of shoulders, your face looking directly straight on at the camera with almost no expression (this will open more castings to you as they can see you playing multiple roles not just one character) and not a lot of Photoshopping, for online you want to sharpen it but when printing it needs to be soft(your photographer will know what soft and sharp is).
Many Times I have seen head shots that include silly poses, hands on face and too much Photoshopping making you look like a model, A casting director does not want glamor shots, if you were shopping online and you order a gift that looks amazing but it arrives not what you expected you will be disappointing, this is what you would be doing to a casting director, you waste your time and most importantly their time.
Make sure it is a recent shot, if you have a beard in the head shot arrive at a casting with a beard same with hair length.
If you plan to apply to jobs in the US use colour shots as this is the most common way over there, always use black and white here in the UK.
one last thing.... don't be cheap, this is your career and cheapness shows.
I hope this can be of some help for you.