turn your container field into a button using the "Insert From Device" script step. You can specify that the type of capture is supposed to be the camera.
Or have a separate button below the container that does the same.
You can even specify whether to use the front or back camera, and what size picture to take.
When you tap on a container field you should get an option to select an input method. It sounds like you might be using custom menus. If you are using custom menus the menus need to allow inserting into a container. Mike's suggestion is the best becasue you can specific what device to use to insert the picture. You might need to attach the button to a script running the Insert from Device script step so you can check the box to perform with Full Access privileges to avoid the custom menu issue.
That worked perfectly.