The Sudoku should be a 9x9 Sudoku. Other types of Sudokus are not supported at the moment. The photo should have at least 8MP. The photo should clearly show a Sudoku with all borders.
This can have several reasons. It could be that it wasn't possible to detect the Sudoku itself in the photo. This can happen due to bad image quality.
This service is designed to process the image file on the fly. Files uploaded are not stored on the server.
Hand written numbers are not recognized properly. The app can be extended by integrating a second AI-model which could recognize hand-written numbers.
Actually, to find a solution for a Sudoku is the fun a Sudoku has to offer. Therefor, offering a service that eliminates the fun by offering an automatic solution doesn't make much sense. But, this app is a pet project of mine that did teach me several technologies a long the way. So, the whole purpose of this app was to provide me obstacles I had to overcome.