Historical seismograms contain a rich harvest of information useful for the study of past earthquakes. It is necessary to extract this information by digitising the analogue records if modern analysis is required. Teseo has been developed for quick and accurate digitisation of seismogram traces from raster files, introducing a vectorisation step based on piecewise cubic Bézier curves. The vectoriser can handle greyscale images stored in a suitable file format and it offers three concurrent vectorisation methods: manual, automatic by colour selection, and automatic by neural networks. The software that implements the methods described is distributed with open source license.