Whilst it is ture that your portfolio will become a vital tool to promote yourself in whatever field it is worth understanding the importance of providing what is asked for or expected.
Many agencies and casting agents will provide information on what they expect and how they expect to receive it. Ignore this at your peril.
Also understand the difference in different parts of the world - an American headshot tends to be quite different from those in the Uk and a composite card in the Us tends to show more portfolio images than those in Europe which often are very "matter of fact" in their presentation.
Remember that we photographers can make you look quite different from your normal "day look" - and this can be the failing of many starting out where their portfolio is an advert for the photographer and not the performer or model.
On a casting the interest is not what you have been but what you can become when they work with you. Yes ok females will still wear basic makeup but not overdone. Boys should try and be themselves, certainly for modeling.
This is covered in more detail in the respective sections.
For an actor performer the most important image they have is that of an accurate HEADSHOT