SummaryAn automatic image analysis system has been developed, that is capable of scanning a large sample area (70 mm × 70 mm) using transmitted light microscopy. The analysis, based on transparent algorithms, successfully discriminates between overlapping and touching fibres, so that sample preparation time is minimized. The system utilizes overlapping image frames to reconstruct partial fibre images and impart unique fibre length information in the range micrometres to millimetres. The software has been made adaptable to enable the accurate measurement of fibre lengths for fibres that curve over many millimetres. Data are presented illustrating the accurate measurement of fibre lengths over a large range of fibre aspect ratios.