what variable type a Video Input Object is in creating a dll.

Hello, I am doing a project to create a dll from matlab and use it in the labview. In the dll, the basic function is output live video, or we can say continuous images. What I am thinking is to define a Video input Object and create three functions to initialize the object, obtain the image and close the object at last. I what to define this video input object as a global variable so that three function can reach it easily. But what data type this Video Input Object is?

For this dll task, is there any other better ideas?

Thanks.