A referance image should contain the amount of detail you yourself can handle, some use cartoon like drawings because you have black lines to define where everything goes, some use blueprints (like for cars) and some use photographs, I have tried all of those three, to me I'd say having a cartoon like drawing is easier for organics, and blueprints for anything precise, photographs are for getting the detail into your model, however many people do use a front and side view of the photographs. Thats another thing, referance images should display the front and side views (top, bottom or/and back if necessary)
Don't ask, I just have to put my friends duck in my sig
