Shapes can be solved on one photo or as many photos as needed. Single photo projects with an unknown camera are very easy to solve with Shapes. To add more complex structure or to get photo texture all around the object, more photos can be added and the same shapes that are visible on those photos can be marked.
Under certain conditions a Shape can even be solved with no photo marking. If a shape has all its free parameters (size parameters and transform parameters) defined or fixed then it will become 3D automatically without any marking. Shape Relations are the tools that allow this to happen. An example of this is a 3D box which is defined by size (w,h,d), by position (Tx,Ty,Tz) and rotation (Rx,Ry,Rz) and if all of those have values before any marking is done the shape can be automatically created and solved in 3D. For example, this might be a box that sits on top of another shape (defines Tz), has a concentric relation (defines Tx and Ty), an aligned relation (defines Rx,Ry and Rz), and relations that define width, height and depth (such as parameter equal relations).