An optical measuring machine, comprising: - an optical detection unit equipped with lighting means configured to generate a light beam along a predetermined optical path, and video capturing means at least partly aligned with the lighting means along the optical path in order to receive the light beam; the video capturing means having a predetermined focal length and a preset visual field; - a support, interposed between the lighting means and the video capturing means, comprising a transparent panel defining a supporting stage for a workpiece to be measured and positioned along The optical path to be crossed by the light beam; - movement means configured to produce a relative movement between the transparent panel and the optical detection unit along a direction of movement at right angles to the optical path in order to allow a plurality of frames of the visual field to be captured along said direction of movement; - a processing unit associated with the video capturing means and configured to combine the frames of the visual field in order to a produce a complete image of a measuring area; characterized in that it comprises a check master connected to the support and placed in a plane located at a distance from the video capturing means equal to the focal length, in order to define an element of comparison for correcting a measuring error, wherein said check master comprises a first segment and a second segment forming a substantially L-shaped structure disposed along the periphery of the transparent panel, at least partly delimiting the measuring area; the processing unit being equipped with a correction module configured to compare a parameter representing the value of a position or dimension of the check master with a stored reference value in order to calculate a correction factor for the captured image, wherein at least said first or second segment is equipped with a plurality of elements of comparison located in succession along a direction of extension of the segment (23a, 23b) itself; the correction module being: configured to compare a value representing the position of each element of comparison in the image captured by the video capturing means with a corresponding stored reference value, and programmed to calculate the image correction factor for each of the elements of comparison, so as to provide different corrections for each zone of the captured image. - an optical detection unit equipped with lighting means configured to generate a light beam along a predetermined optical path, and video capturing means at least partly aligned with the lighting means along the optical path in order to receive the light beam; the video capturing means having a predetermined focal length and a preset visual field; - a support, interposed between the lighting means and the video capturing means, comprising a transparent panel defining a supporting stage for a workpiece to be measured and positioned along The optical path to be crossed by the light beam; - movement means configured to produce a relative movement between the transparent panel and the optical detection unit along a direction of movement at right angles to the optical path in order to allow a plurality of frames of the visual field to be captured along said direction of movement; - a processing unit associated with the video capturing means and configured to combine the frames of the visual field in order to a produce a complete image of a measuring area; configured to compare a value representing the position of each element of comparison in the image captured by the video capturing means with a corresponding stored reference value, and programmed to calculate the image correction factor for each of the elements of comparison, so as to provide different corrections for each zone of the captured image.