All-cellulose composites (ACCs) were prepared from filter paper via partial dissolution in the ionic liquid 1-ethyl-3-methylimidazolium acetate, and material tensile properties were investigated using various approaches. One is based on data directly taken from a tensile testing machine, and the other uses two-cameras stereovision with digital image correlation (DIC) technique. In the latter case, virtual extensometer with different locations on the sample and averaging over sample surface were tested. Nominal and true stress–strain dependences were built and Young's modulus, tensile strength, elongation at maximal stress and toughness were evaluated as a function of ACC density. A minor difference was observed for the stress–strain dependences derived from different approaches which use the DIC technique, most probably because of low ACC deformation. However, the results reveal that the nominal stress–strain curve from DIC is significantly different from that which is directly derived from the data provided by machine sensors thus strongly impacting Young’s modulus and elongation at break values. This study provides an insight into the evaluation of the mechanical properties of ACCs. Graphic abstract