  We consider the problem of scale detection in images where a region of
interest is present together with a measurement tool (e.g. a ruler). For the
segmentation part, we focus on the graph based method by Flenner and Bertozzi
which reinterprets classical continuous Ginzburg-Landau minimisation models in
a totally discrete framework. To overcome the numerical difficulties due to the
large size of the images considered we use matrix completion and splitting
techniques. The scale on the measurement tool is detected via a Hough transform
based algorithm. The method is then applied to some measurement tasks arising
in real-world applications such as zoology, medicine and archaeology.
