The requisite image for all models and actors is a close-up head and shoulders portrait. Agencies and anyone casting, will not be impressed with anything too distracting or undiscernible. They're looking for an honest and clear image.
With applications of make-up, it's best to keep it light and natural, no sunglasses, hats, etc.
For attire, it's recommended to keep it simple, no busy patterns, or flashy jewelry or accessories. When a casting agent is quickly parsing through a stack of prospects the tactic is that they notice you, not to what you're wearing.
Building your portfolio can be an entirely different process. Often a casting agent has noticed you and wants to see more. A porfolio can include a variety of creative images showcasing versatility and demostrating an ability to take on various roles and different looks.