fSpy is open source software and totally free to download and use. But just in case you think it makes sense to pay for fSpy, here's a donate button! Pay as much or as little as you want.

Tutorial This tutorial will walk you through the example project included in the app. Make sure you’ve gone through the basics before proceeding. Vanishing points and the 3D origin Open the example …

fSpy uses the position of vanishing points to estimate camera parameters. A vanishing point is specified using two line segements aligned with features in the image that correspond to parallel lines in 3D …