One of the most critical aspects of integrating the various CG elements in your scene is camera matching. Camera matching is the process of estimating camera parameters from certain features in an image.
To achieve the correct perspective, crucial details from the backplate, such as resolution, camera model, and, notably, focal length, must be considered. Unfortunately, many internet-sourced images lack this essential information, particularly if they are in JPEG format, which can complicate the camera matching procedure.
In these cases, it is possible to use a software called fSpy.
Fspy is an open-source software tool used for camera matching and perspective matching in visual effects workflows. It helps artists align virtual objects and scenes with real-world footage by reverse-engineering the camera parameters and lens characteristics from a single picture.
In this tutorial, I will guide you through the process of using fSpy to calculate the focal length and use it in your Maya scene.
https://fspy.io/
Federico Arculeo – 3D VFX Tutor at Escape Studios
THE ART OF VISUAL EFFECTS AT ESCAPE STUDIOS 