1. A method for optically scanning a three-dimensional object with a dental 3D camera that operates in accordance with a triangulation procedure to acquire a plurality of images of the object, the method comprising: forming at least one comparative signal based on at least two images of the object acquired by the camera while at least one pattern is projected on the object; and determining at least one camera shake index based on the at least one comparative signal, wherein the images include a plurality of pixels having coordinates showing levels of intensity or grayness, the at least one comparative signal comprises a plurality of pixels, and the forming of the at least one comparative signal includes dividing or subtracting two images of the at least one pattern of respective phase positions to obtain a quotient or difference, respectively, formed for levels of intensity of those images on a pixel-by-pixel basis.