In an age of internet scamming, it helps when the potential purchaser of your book can develop an emotional link with you and your face becomes recognizable to them.
This is not the time to use a picture that is taken with your smart phone. Engaging the services of a professional photographer will be one of the best investments that you can make in your writing career. The professional is knowledgeable about lighting and is able to position you in the best possible pose to produce a quality image of you. He/she is able to focus the camera in such a way that you are truly the focus of the picture and all unflattering distractions are blurred out. Always request a 300 dpi image file – which can be sized down for the web. Sometimes, a camera phone used is not at the maximum setting, and let’s say that you get a really good picture, it is really sad not to be able to use it for your promotional material.
There are some persons who believe that they should only use one picture for their entire writing life. Wrong. Your audience needs to be able to recognize you. What is the point of using a picture that is three or four years old and you no longer look like the picture? That alone can come across as a deception to your readers. If you are the kind of person who has a new look every 2 months, then as you grow and change, your readers need to be able to connect with you through the changes.
You are not going to be an unknown forever, get it right the first time, so that you do not have to scramble to fix things.